xref: /illumos-gate/usr/src/uts/common/fs/zfs/zil.c (revision b6031810)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
23  * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
24  * Copyright (c) 2014 Integros [integros.com]
25  */
26 
27 /* Portions Copyright 2010 Robert Milkowski */
28 
29 #include <sys/zfs_context.h>
30 #include <sys/spa.h>
31 #include <sys/spa_impl.h>
32 #include <sys/dmu.h>
33 #include <sys/zap.h>
34 #include <sys/arc.h>
35 #include <sys/stat.h>
36 #include <sys/resource.h>
37 #include <sys/zil.h>
38 #include <sys/zil_impl.h>
39 #include <sys/dsl_dataset.h>
40 #include <sys/vdev_impl.h>
41 #include <sys/dmu_tx.h>
42 #include <sys/dsl_pool.h>
43 #include <sys/abd.h>
44 
45 /*
46  * The ZFS Intent Log (ZIL) saves "transaction records" (itxs) of system
47  * calls that change the file system. Each itx has enough information to
48  * be able to replay them after a system crash, power loss, or
49  * equivalent failure mode. These are stored in memory until either:
50  *
51  *   1. they are committed to the pool by the DMU transaction group
52  *      (txg), at which point they can be discarded; or
53  *   2. they are committed to the on-disk ZIL for the dataset being
54  *      modified (e.g. due to an fsync, O_DSYNC, or other synchronous
55  *      requirement).
56  *
57  * In the event of a crash or power loss, the itxs contained by each
58  * dataset's on-disk ZIL will be replayed when that dataset is first
59  * instantianted (e.g. if the dataset is a normal fileystem, when it is
60  * first mounted).
61  *
62  * As hinted at above, there is one ZIL per dataset (both the in-memory
63  * representation, and the on-disk representation). The on-disk format
64  * consists of 3 parts:
65  *
66  * 	- a single, per-dataset, ZIL header; which points to a chain of
67  * 	- zero or more ZIL blocks; each of which contains
68  * 	- zero or more ZIL records
69  *
70  * A ZIL record holds the information necessary to replay a single
71  * system call transaction. A ZIL block can hold many ZIL records, and
72  * the blocks are chained together, similarly to a singly linked list.
73  *
74  * Each ZIL block contains a block pointer (blkptr_t) to the next ZIL
75  * block in the chain, and the ZIL header points to the first block in
76  * the chain.
77  *
78  * Note, there is not a fixed place in the pool to hold these ZIL
79  * blocks; they are dynamically allocated and freed as needed from the
80  * blocks available on the pool, though they can be preferentially
81  * allocated from a dedicated "log" vdev.
82  */
83 
84 /*
85  * This controls the amount of time that a ZIL block (lwb) will remain
86  * "open" when it isn't "full", and it has a thread waiting for it to be
87  * committed to stable storage. Please refer to the zil_commit_waiter()
88  * function (and the comments within it) for more details.
89  */
90 int zfs_commit_timeout_pct = 5;
91 
92 /*
93  * Disable intent logging replay.  This global ZIL switch affects all pools.
94  */
95 int zil_replay_disable = 0;
96 
97 /*
98  * Tunable parameter for debugging or performance analysis.  Setting
99  * zfs_nocacheflush will cause corruption on power loss if a volatile
100  * out-of-order write cache is enabled.
101  */
102 boolean_t zfs_nocacheflush = B_FALSE;
103 
104 /*
105  * Limit SLOG write size per commit executed with synchronous priority.
106  * Any writes above that will be executed with lower (asynchronous) priority
107  * to limit potential SLOG device abuse by single active ZIL writer.
108  */
109 uint64_t zil_slog_bulk = 768 * 1024;
110 
111 static kmem_cache_t *zil_lwb_cache;
112 static kmem_cache_t *zil_zcw_cache;
113 
114 static void zil_async_to_sync(zilog_t *zilog, uint64_t foid);
115 
116 #define	LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
117     sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))
118 
119 static int
120 zil_bp_compare(const void *x1, const void *x2)
121 {
122 	const dva_t *dva1 = &((zil_bp_node_t *)x1)->zn_dva;
123 	const dva_t *dva2 = &((zil_bp_node_t *)x2)->zn_dva;
124 
125 	if (DVA_GET_VDEV(dva1) < DVA_GET_VDEV(dva2))
126 		return (-1);
127 	if (DVA_GET_VDEV(dva1) > DVA_GET_VDEV(dva2))
128 		return (1);
129 
130 	if (DVA_GET_OFFSET(dva1) < DVA_GET_OFFSET(dva2))
131 		return (-1);
132 	if (DVA_GET_OFFSET(dva1) > DVA_GET_OFFSET(dva2))
133 		return (1);
134 
135 	return (0);
136 }
137 
138 static void
139 zil_bp_tree_init(zilog_t *zilog)
140 {
141 	avl_create(&zilog->zl_bp_tree, zil_bp_compare,
142 	    sizeof (zil_bp_node_t), offsetof(zil_bp_node_t, zn_node));
143 }
144 
145 static void
146 zil_bp_tree_fini(zilog_t *zilog)
147 {
148 	avl_tree_t *t = &zilog->zl_bp_tree;
149 	zil_bp_node_t *zn;
150 	void *cookie = NULL;
151 
152 	while ((zn = avl_destroy_nodes(t, &cookie)) != NULL)
153 		kmem_free(zn, sizeof (zil_bp_node_t));
154 
155 	avl_destroy(t);
156 }
157 
158 int
159 zil_bp_tree_add(zilog_t *zilog, const blkptr_t *bp)
160 {
161 	avl_tree_t *t = &zilog->zl_bp_tree;
162 	const dva_t *dva;
163 	zil_bp_node_t *zn;
164 	avl_index_t where;
165 
166 	if (BP_IS_EMBEDDED(bp))
167 		return (0);
168 
169 	dva = BP_IDENTITY(bp);
170 
171 	if (avl_find(t, dva, &where) != NULL)
172 		return (SET_ERROR(EEXIST));
173 
174 	zn = kmem_alloc(sizeof (zil_bp_node_t), KM_SLEEP);
175 	zn->zn_dva = *dva;
176 	avl_insert(t, zn, where);
177 
178 	return (0);
179 }
180 
181 static zil_header_t *
182 zil_header_in_syncing_context(zilog_t *zilog)
183 {
184 	return ((zil_header_t *)zilog->zl_header);
185 }
186 
187 static void
188 zil_init_log_chain(zilog_t *zilog, blkptr_t *bp)
189 {
190 	zio_cksum_t *zc = &bp->blk_cksum;
191 
192 	zc->zc_word[ZIL_ZC_GUID_0] = spa_get_random(-1ULL);
193 	zc->zc_word[ZIL_ZC_GUID_1] = spa_get_random(-1ULL);
194 	zc->zc_word[ZIL_ZC_OBJSET] = dmu_objset_id(zilog->zl_os);
195 	zc->zc_word[ZIL_ZC_SEQ] = 1ULL;
196 }
197 
198 /*
199  * Read a log block and make sure it's valid.
200  */
201 static int
202 zil_read_log_block(zilog_t *zilog, const blkptr_t *bp, blkptr_t *nbp, void *dst,
203     char **end)
204 {
205 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
206 	arc_flags_t aflags = ARC_FLAG_WAIT;
207 	arc_buf_t *abuf = NULL;
208 	zbookmark_phys_t zb;
209 	int error;
210 
211 	if (zilog->zl_header->zh_claim_txg == 0)
212 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
213 
214 	if (!(zilog->zl_header->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
215 		zio_flags |= ZIO_FLAG_SPECULATIVE;
216 
217 	SET_BOOKMARK(&zb, bp->blk_cksum.zc_word[ZIL_ZC_OBJSET],
218 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);
219 
220 	error = arc_read(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
221 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
222 
223 	if (error == 0) {
224 		zio_cksum_t cksum = bp->blk_cksum;
225 
226 		/*
227 		 * Validate the checksummed log block.
228 		 *
229 		 * Sequence numbers should be... sequential.  The checksum
230 		 * verifier for the next block should be bp's checksum plus 1.
231 		 *
232 		 * Also check the log chain linkage and size used.
233 		 */
234 		cksum.zc_word[ZIL_ZC_SEQ]++;
235 
236 		if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
237 			zil_chain_t *zilc = abuf->b_data;
238 			char *lr = (char *)(zilc + 1);
239 			uint64_t len = zilc->zc_nused - sizeof (zil_chain_t);
240 
241 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
242 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk)) {
243 				error = SET_ERROR(ECKSUM);
244 			} else {
245 				ASSERT3U(len, <=, SPA_OLD_MAXBLOCKSIZE);
246 				bcopy(lr, dst, len);
247 				*end = (char *)dst + len;
248 				*nbp = zilc->zc_next_blk;
249 			}
250 		} else {
251 			char *lr = abuf->b_data;
252 			uint64_t size = BP_GET_LSIZE(bp);
253 			zil_chain_t *zilc = (zil_chain_t *)(lr + size) - 1;
254 
255 			if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
256 			    sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk) ||
257 			    (zilc->zc_nused > (size - sizeof (*zilc)))) {
258 				error = SET_ERROR(ECKSUM);
259 			} else {
260 				ASSERT3U(zilc->zc_nused, <=,
261 				    SPA_OLD_MAXBLOCKSIZE);
262 				bcopy(lr, dst, zilc->zc_nused);
263 				*end = (char *)dst + zilc->zc_nused;
264 				*nbp = zilc->zc_next_blk;
265 			}
266 		}
267 
268 		arc_buf_destroy(abuf, &abuf);
269 	}
270 
271 	return (error);
272 }
273 
274 /*
275  * Read a TX_WRITE log data block.
276  */
277 static int
278 zil_read_log_data(zilog_t *zilog, const lr_write_t *lr, void *wbuf)
279 {
280 	enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
281 	const blkptr_t *bp = &lr->lr_blkptr;
282 	arc_flags_t aflags = ARC_FLAG_WAIT;
283 	arc_buf_t *abuf = NULL;
284 	zbookmark_phys_t zb;
285 	int error;
286 
287 	if (BP_IS_HOLE(bp)) {
288 		if (wbuf != NULL)
289 			bzero(wbuf, MAX(BP_GET_LSIZE(bp), lr->lr_length));
290 		return (0);
291 	}
292 
293 	if (zilog->zl_header->zh_claim_txg == 0)
294 		zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;
295 
296 	SET_BOOKMARK(&zb, dmu_objset_id(zilog->zl_os), lr->lr_foid,
297 	    ZB_ZIL_LEVEL, lr->lr_offset / BP_GET_LSIZE(bp));
298 
299 	error = arc_read(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
300 	    ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);
301 
302 	if (error == 0) {
303 		if (wbuf != NULL)
304 			bcopy(abuf->b_data, wbuf, arc_buf_size(abuf));
305 		arc_buf_destroy(abuf, &abuf);
306 	}
307 
308 	return (error);
309 }
310 
311 /*
312  * Parse the intent log, and call parse_func for each valid record within.
313  */
314 int
315 zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
316     zil_parse_lr_func_t *parse_lr_func, void *arg, uint64_t txg)
317 {
318 	const zil_header_t *zh = zilog->zl_header;
319 	boolean_t claimed = !!zh->zh_claim_txg;
320 	uint64_t claim_blk_seq = claimed ? zh->zh_claim_blk_seq : UINT64_MAX;
321 	uint64_t claim_lr_seq = claimed ? zh->zh_claim_lr_seq : UINT64_MAX;
322 	uint64_t max_blk_seq = 0;
323 	uint64_t max_lr_seq = 0;
324 	uint64_t blk_count = 0;
325 	uint64_t lr_count = 0;
326 	blkptr_t blk, next_blk;
327 	char *lrbuf, *lrp;
328 	int error = 0;
329 
330 	/*
331 	 * Old logs didn't record the maximum zh_claim_lr_seq.
332 	 */
333 	if (!(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
334 		claim_lr_seq = UINT64_MAX;
335 
336 	/*
337 	 * Starting at the block pointed to by zh_log we read the log chain.
338 	 * For each block in the chain we strongly check that block to
339 	 * ensure its validity.  We stop when an invalid block is found.
340 	 * For each block pointer in the chain we call parse_blk_func().
341 	 * For each record in each valid block we call parse_lr_func().
342 	 * If the log has been claimed, stop if we encounter a sequence
343 	 * number greater than the highest claimed sequence number.
344 	 */
345 	lrbuf = zio_buf_alloc(SPA_OLD_MAXBLOCKSIZE);
346 	zil_bp_tree_init(zilog);
347 
348 	for (blk = zh->zh_log; !BP_IS_HOLE(&blk); blk = next_blk) {
349 		uint64_t blk_seq = blk.blk_cksum.zc_word[ZIL_ZC_SEQ];
350 		int reclen;
351 		char *end;
352 
353 		if (blk_seq > claim_blk_seq)
354 			break;
355 		if ((error = parse_blk_func(zilog, &blk, arg, txg)) != 0)
356 			break;
357 		ASSERT3U(max_blk_seq, <, blk_seq);
358 		max_blk_seq = blk_seq;
359 		blk_count++;
360 
361 		if (max_lr_seq == claim_lr_seq && max_blk_seq == claim_blk_seq)
362 			break;
363 
364 		error = zil_read_log_block(zilog, &blk, &next_blk, lrbuf, &end);
365 		if (error != 0)
366 			break;
367 
368 		for (lrp = lrbuf; lrp < end; lrp += reclen) {
369 			lr_t *lr = (lr_t *)lrp;
370 			reclen = lr->lrc_reclen;
371 			ASSERT3U(reclen, >=, sizeof (lr_t));
372 			if (lr->lrc_seq > claim_lr_seq)
373 				goto done;
374 			if ((error = parse_lr_func(zilog, lr, arg, txg)) != 0)
375 				goto done;
376 			ASSERT3U(max_lr_seq, <, lr->lrc_seq);
377 			max_lr_seq = lr->lrc_seq;
378 			lr_count++;
379 		}
380 	}
381 done:
382 	zilog->zl_parse_error = error;
383 	zilog->zl_parse_blk_seq = max_blk_seq;
384 	zilog->zl_parse_lr_seq = max_lr_seq;
385 	zilog->zl_parse_blk_count = blk_count;
386 	zilog->zl_parse_lr_count = lr_count;
387 
388 	ASSERT(!claimed || !(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID) ||
389 	    (max_blk_seq == claim_blk_seq && max_lr_seq == claim_lr_seq));
390 
391 	zil_bp_tree_fini(zilog);
392 	zio_buf_free(lrbuf, SPA_OLD_MAXBLOCKSIZE);
393 
394 	return (error);
395 }
396 
397 /* ARGSUSED */
398 static int
399 zil_clear_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
400 {
401 	ASSERT(!BP_IS_HOLE(bp));
402 
403 	/*
404 	 * As we call this function from the context of a rewind to a
405 	 * checkpoint, each ZIL block whose txg is later than the txg
406 	 * that we rewind to is invalid. Thus, we return -1 so
407 	 * zil_parse() doesn't attempt to read it.
408 	 */
409 	if (bp->blk_birth >= first_txg)
410 		return (-1);
411 
412 	if (zil_bp_tree_add(zilog, bp) != 0)
413 		return (0);
414 
415 	zio_free(zilog->zl_spa, first_txg, bp);
416 	return (0);
417 }
418 
419 /* ARGSUSED */
420 static int
421 zil_noop_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
422 {
423 	return (0);
424 }
425 
426 static int
427 zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
428 {
429 	/*
430 	 * Claim log block if not already committed and not already claimed.
431 	 * If tx == NULL, just verify that the block is claimable.
432 	 */
433 	if (BP_IS_HOLE(bp) || bp->blk_birth < first_txg ||
434 	    zil_bp_tree_add(zilog, bp) != 0)
435 		return (0);
436 
437 	return (zio_wait(zio_claim(NULL, zilog->zl_spa,
438 	    tx == NULL ? 0 : first_txg, bp, spa_claim_notify, NULL,
439 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB)));
440 }
441 
442 static int
443 zil_claim_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
444 {
445 	lr_write_t *lr = (lr_write_t *)lrc;
446 	int error;
447 
448 	if (lrc->lrc_txtype != TX_WRITE)
449 		return (0);
450 
451 	/*
452 	 * If the block is not readable, don't claim it.  This can happen
453 	 * in normal operation when a log block is written to disk before
454 	 * some of the dmu_sync() blocks it points to.  In this case, the
455 	 * transaction cannot have been committed to anyone (we would have
456 	 * waited for all writes to be stable first), so it is semantically
457 	 * correct to declare this the end of the log.
458 	 */
459 	if (lr->lr_blkptr.blk_birth >= first_txg &&
460 	    (error = zil_read_log_data(zilog, lr, NULL)) != 0)
461 		return (error);
462 	return (zil_claim_log_block(zilog, &lr->lr_blkptr, tx, first_txg));
463 }
464 
465 /* ARGSUSED */
466 static int
467 zil_free_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t claim_txg)
468 {
469 	zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
470 
471 	return (0);
472 }
473 
474 static int
475 zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
476 {
477 	lr_write_t *lr = (lr_write_t *)lrc;
478 	blkptr_t *bp = &lr->lr_blkptr;
479 
480 	/*
481 	 * If we previously claimed it, we need to free it.
482 	 */
483 	if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE &&
484 	    bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0 &&
485 	    !BP_IS_HOLE(bp))
486 		zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);
487 
488 	return (0);
489 }
490 
491 static int
492 zil_lwb_vdev_compare(const void *x1, const void *x2)
493 {
494 	const uint64_t v1 = ((zil_vdev_node_t *)x1)->zv_vdev;
495 	const uint64_t v2 = ((zil_vdev_node_t *)x2)->zv_vdev;
496 
497 	if (v1 < v2)
498 		return (-1);
499 	if (v1 > v2)
500 		return (1);
501 
502 	return (0);
503 }
504 
505 static lwb_t *
506 zil_alloc_lwb(zilog_t *zilog, blkptr_t *bp, boolean_t slog, uint64_t txg)
507 {
508 	lwb_t *lwb;
509 
510 	lwb = kmem_cache_alloc(zil_lwb_cache, KM_SLEEP);
511 	lwb->lwb_zilog = zilog;
512 	lwb->lwb_blk = *bp;
513 	lwb->lwb_slog = slog;
514 	lwb->lwb_state = LWB_STATE_CLOSED;
515 	lwb->lwb_buf = zio_buf_alloc(BP_GET_LSIZE(bp));
516 	lwb->lwb_max_txg = txg;
517 	lwb->lwb_write_zio = NULL;
518 	lwb->lwb_root_zio = NULL;
519 	lwb->lwb_tx = NULL;
520 	lwb->lwb_issued_timestamp = 0;
521 	if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
522 		lwb->lwb_nused = sizeof (zil_chain_t);
523 		lwb->lwb_sz = BP_GET_LSIZE(bp);
524 	} else {
525 		lwb->lwb_nused = 0;
526 		lwb->lwb_sz = BP_GET_LSIZE(bp) - sizeof (zil_chain_t);
527 	}
528 
529 	mutex_enter(&zilog->zl_lock);
530 	list_insert_tail(&zilog->zl_lwb_list, lwb);
531 	mutex_exit(&zilog->zl_lock);
532 
533 	ASSERT(!MUTEX_HELD(&lwb->lwb_vdev_lock));
534 	ASSERT(avl_is_empty(&lwb->lwb_vdev_tree));
535 	VERIFY(list_is_empty(&lwb->lwb_waiters));
536 
537 	return (lwb);
538 }
539 
540 static void
541 zil_free_lwb(zilog_t *zilog, lwb_t *lwb)
542 {
543 	ASSERT(MUTEX_HELD(&zilog->zl_lock));
544 	ASSERT(!MUTEX_HELD(&lwb->lwb_vdev_lock));
545 	VERIFY(list_is_empty(&lwb->lwb_waiters));
546 	ASSERT(avl_is_empty(&lwb->lwb_vdev_tree));
547 	ASSERT3P(lwb->lwb_write_zio, ==, NULL);
548 	ASSERT3P(lwb->lwb_root_zio, ==, NULL);
549 	ASSERT3U(lwb->lwb_max_txg, <=, spa_syncing_txg(zilog->zl_spa));
550 	ASSERT(lwb->lwb_state == LWB_STATE_CLOSED ||
551 	    lwb->lwb_state == LWB_STATE_DONE);
552 
553 	/*
554 	 * Clear the zilog's field to indicate this lwb is no longer
555 	 * valid, and prevent use-after-free errors.
556 	 */
557 	if (zilog->zl_last_lwb_opened == lwb)
558 		zilog->zl_last_lwb_opened = NULL;
559 
560 	kmem_cache_free(zil_lwb_cache, lwb);
561 }
562 
563 /*
564  * Called when we create in-memory log transactions so that we know
565  * to cleanup the itxs at the end of spa_sync().
566  */
567 void
568 zilog_dirty(zilog_t *zilog, uint64_t txg)
569 {
570 	dsl_pool_t *dp = zilog->zl_dmu_pool;
571 	dsl_dataset_t *ds = dmu_objset_ds(zilog->zl_os);
572 
573 	ASSERT(spa_writeable(zilog->zl_spa));
574 
575 	if (ds->ds_is_snapshot)
576 		panic("dirtying snapshot!");
577 
578 	if (txg_list_add(&dp->dp_dirty_zilogs, zilog, txg)) {
579 		/* up the hold count until we can be written out */
580 		dmu_buf_add_ref(ds->ds_dbuf, zilog);
581 
582 		zilog->zl_dirty_max_txg = MAX(txg, zilog->zl_dirty_max_txg);
583 	}
584 }
585 
586 /*
587  * Determine if the zil is dirty in the specified txg. Callers wanting to
588  * ensure that the dirty state does not change must hold the itxg_lock for
589  * the specified txg. Holding the lock will ensure that the zil cannot be
590  * dirtied (zil_itx_assign) or cleaned (zil_clean) while we check its current
591  * state.
592  */
593 boolean_t
594 zilog_is_dirty_in_txg(zilog_t *zilog, uint64_t txg)
595 {
596 	dsl_pool_t *dp = zilog->zl_dmu_pool;
597 
598 	if (txg_list_member(&dp->dp_dirty_zilogs, zilog, txg & TXG_MASK))
599 		return (B_TRUE);
600 	return (B_FALSE);
601 }
602 
603 /*
604  * Determine if the zil is dirty. The zil is considered dirty if it has
605  * any pending itx records that have not been cleaned by zil_clean().
606  */
607 boolean_t
608 zilog_is_dirty(zilog_t *zilog)
609 {
610 	dsl_pool_t *dp = zilog->zl_dmu_pool;
611 
612 	for (int t = 0; t < TXG_SIZE; t++) {
613 		if (txg_list_member(&dp->dp_dirty_zilogs, zilog, t))
614 			return (B_TRUE);
615 	}
616 	return (B_FALSE);
617 }
618 
619 /*
620  * Create an on-disk intent log.
621  */
622 static lwb_t *
623 zil_create(zilog_t *zilog)
624 {
625 	const zil_header_t *zh = zilog->zl_header;
626 	lwb_t *lwb = NULL;
627 	uint64_t txg = 0;
628 	dmu_tx_t *tx = NULL;
629 	blkptr_t blk;
630 	int error = 0;
631 	boolean_t slog = FALSE;
632 
633 	/*
634 	 * Wait for any previous destroy to complete.
635 	 */
636 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
637 
638 	ASSERT(zh->zh_claim_txg == 0);
639 	ASSERT(zh->zh_replay_seq == 0);
640 
641 	blk = zh->zh_log;
642 
643 	/*
644 	 * Allocate an initial log block if:
645 	 *    - there isn't one already
646 	 *    - the existing block is the wrong endianess
647 	 */
648 	if (BP_IS_HOLE(&blk) || BP_SHOULD_BYTESWAP(&blk)) {
649 		tx = dmu_tx_create(zilog->zl_os);
650 		VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
651 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
652 		txg = dmu_tx_get_txg(tx);
653 
654 		if (!BP_IS_HOLE(&blk)) {
655 			zio_free(zilog->zl_spa, txg, &blk);
656 			BP_ZERO(&blk);
657 		}
658 
659 		error = zio_alloc_zil(zilog->zl_spa,
660 		    zilog->zl_os->os_dsl_dataset->ds_object, txg, &blk, NULL,
661 		    ZIL_MIN_BLKSZ, &slog);
662 
663 		if (error == 0)
664 			zil_init_log_chain(zilog, &blk);
665 	}
666 
667 	/*
668 	 * Allocate a log write block (lwb) for the first log block.
669 	 */
670 	if (error == 0)
671 		lwb = zil_alloc_lwb(zilog, &blk, slog, txg);
672 
673 	/*
674 	 * If we just allocated the first log block, commit our transaction
675 	 * and wait for zil_sync() to stuff the block poiner into zh_log.
676 	 * (zh is part of the MOS, so we cannot modify it in open context.)
677 	 */
678 	if (tx != NULL) {
679 		dmu_tx_commit(tx);
680 		txg_wait_synced(zilog->zl_dmu_pool, txg);
681 	}
682 
683 	ASSERT(bcmp(&blk, &zh->zh_log, sizeof (blk)) == 0);
684 
685 	return (lwb);
686 }
687 
688 /*
689  * In one tx, free all log blocks and clear the log header. If keep_first
690  * is set, then we're replaying a log with no content. We want to keep the
691  * first block, however, so that the first synchronous transaction doesn't
692  * require a txg_wait_synced() in zil_create(). We don't need to
693  * txg_wait_synced() here either when keep_first is set, because both
694  * zil_create() and zil_destroy() will wait for any in-progress destroys
695  * to complete.
696  */
697 void
698 zil_destroy(zilog_t *zilog, boolean_t keep_first)
699 {
700 	const zil_header_t *zh = zilog->zl_header;
701 	lwb_t *lwb;
702 	dmu_tx_t *tx;
703 	uint64_t txg;
704 
705 	/*
706 	 * Wait for any previous destroy to complete.
707 	 */
708 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
709 
710 	zilog->zl_old_header = *zh;		/* debugging aid */
711 
712 	if (BP_IS_HOLE(&zh->zh_log))
713 		return;
714 
715 	tx = dmu_tx_create(zilog->zl_os);
716 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
717 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
718 	txg = dmu_tx_get_txg(tx);
719 
720 	mutex_enter(&zilog->zl_lock);
721 
722 	ASSERT3U(zilog->zl_destroy_txg, <, txg);
723 	zilog->zl_destroy_txg = txg;
724 	zilog->zl_keep_first = keep_first;
725 
726 	if (!list_is_empty(&zilog->zl_lwb_list)) {
727 		ASSERT(zh->zh_claim_txg == 0);
728 		VERIFY(!keep_first);
729 		while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
730 			list_remove(&zilog->zl_lwb_list, lwb);
731 			if (lwb->lwb_buf != NULL)
732 				zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
733 			zio_free(zilog->zl_spa, txg, &lwb->lwb_blk);
734 			zil_free_lwb(zilog, lwb);
735 		}
736 	} else if (!keep_first) {
737 		zil_destroy_sync(zilog, tx);
738 	}
739 	mutex_exit(&zilog->zl_lock);
740 
741 	dmu_tx_commit(tx);
742 }
743 
744 void
745 zil_destroy_sync(zilog_t *zilog, dmu_tx_t *tx)
746 {
747 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
748 	(void) zil_parse(zilog, zil_free_log_block,
749 	    zil_free_log_record, tx, zilog->zl_header->zh_claim_txg);
750 }
751 
752 int
753 zil_claim(dsl_pool_t *dp, dsl_dataset_t *ds, void *txarg)
754 {
755 	dmu_tx_t *tx = txarg;
756 	zilog_t *zilog;
757 	uint64_t first_txg;
758 	zil_header_t *zh;
759 	objset_t *os;
760 	int error;
761 
762 	error = dmu_objset_own_obj(dp, ds->ds_object,
763 	    DMU_OST_ANY, B_FALSE, FTAG, &os);
764 	if (error != 0) {
765 		/*
766 		 * EBUSY indicates that the objset is inconsistent, in which
767 		 * case it can not have a ZIL.
768 		 */
769 		if (error != EBUSY) {
770 			cmn_err(CE_WARN, "can't open objset for %llu, error %u",
771 			    (unsigned long long)ds->ds_object, error);
772 		}
773 		return (0);
774 	}
775 
776 	zilog = dmu_objset_zil(os);
777 	zh = zil_header_in_syncing_context(zilog);
778 	ASSERT3U(tx->tx_txg, ==, spa_first_txg(zilog->zl_spa));
779 	first_txg = spa_min_claim_txg(zilog->zl_spa);
780 
781 	/*
782 	 * If the spa_log_state is not set to be cleared, check whether
783 	 * the current uberblock is a checkpoint one and if the current
784 	 * header has been claimed before moving on.
785 	 *
786 	 * If the current uberblock is a checkpointed uberblock then
787 	 * one of the following scenarios took place:
788 	 *
789 	 * 1] We are currently rewinding to the checkpoint of the pool.
790 	 * 2] We crashed in the middle of a checkpoint rewind but we
791 	 *    did manage to write the checkpointed uberblock to the
792 	 *    vdev labels, so when we tried to import the pool again
793 	 *    the checkpointed uberblock was selected from the import
794 	 *    procedure.
795 	 *
796 	 * In both cases we want to zero out all the ZIL blocks, except
797 	 * the ones that have been claimed at the time of the checkpoint
798 	 * (their zh_claim_txg != 0). The reason is that these blocks
799 	 * may be corrupted since we may have reused their locations on
800 	 * disk after we took the checkpoint.
801 	 *
802 	 * We could try to set spa_log_state to SPA_LOG_CLEAR earlier
803 	 * when we first figure out whether the current uberblock is
804 	 * checkpointed or not. Unfortunately, that would discard all
805 	 * the logs, including the ones that are claimed, and we would
806 	 * leak space.
807 	 */
808 	if (spa_get_log_state(zilog->zl_spa) == SPA_LOG_CLEAR ||
809 	    (zilog->zl_spa->spa_uberblock.ub_checkpoint_txg != 0 &&
810 	    zh->zh_claim_txg == 0)) {
811 		if (!BP_IS_HOLE(&zh->zh_log)) {
812 			(void) zil_parse(zilog, zil_clear_log_block,
813 			    zil_noop_log_record, tx, first_txg);
814 		}
815 		BP_ZERO(&zh->zh_log);
816 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
817 		dmu_objset_disown(os, FTAG);
818 		return (0);
819 	}
820 
821 	/*
822 	 * If we are not rewinding and opening the pool normally, then
823 	 * the min_claim_txg should be equal to the first txg of the pool.
824 	 */
825 	ASSERT3U(first_txg, ==, spa_first_txg(zilog->zl_spa));
826 
827 	/*
828 	 * Claim all log blocks if we haven't already done so, and remember
829 	 * the highest claimed sequence number.  This ensures that if we can
830 	 * read only part of the log now (e.g. due to a missing device),
831 	 * but we can read the entire log later, we will not try to replay
832 	 * or destroy beyond the last block we successfully claimed.
833 	 */
834 	ASSERT3U(zh->zh_claim_txg, <=, first_txg);
835 	if (zh->zh_claim_txg == 0 && !BP_IS_HOLE(&zh->zh_log)) {
836 		(void) zil_parse(zilog, zil_claim_log_block,
837 		    zil_claim_log_record, tx, first_txg);
838 		zh->zh_claim_txg = first_txg;
839 		zh->zh_claim_blk_seq = zilog->zl_parse_blk_seq;
840 		zh->zh_claim_lr_seq = zilog->zl_parse_lr_seq;
841 		if (zilog->zl_parse_lr_count || zilog->zl_parse_blk_count > 1)
842 			zh->zh_flags |= ZIL_REPLAY_NEEDED;
843 		zh->zh_flags |= ZIL_CLAIM_LR_SEQ_VALID;
844 		dsl_dataset_dirty(dmu_objset_ds(os), tx);
845 	}
846 
847 	ASSERT3U(first_txg, ==, (spa_last_synced_txg(zilog->zl_spa) + 1));
848 	dmu_objset_disown(os, FTAG);
849 	return (0);
850 }
851 
852 /*
853  * Check the log by walking the log chain.
854  * Checksum errors are ok as they indicate the end of the chain.
855  * Any other error (no device or read failure) returns an error.
856  */
857 /* ARGSUSED */
858 int
859 zil_check_log_chain(dsl_pool_t *dp, dsl_dataset_t *ds, void *tx)
860 {
861 	zilog_t *zilog;
862 	objset_t *os;
863 	blkptr_t *bp;
864 	int error;
865 
866 	ASSERT(tx == NULL);
867 
868 	error = dmu_objset_from_ds(ds, &os);
869 	if (error != 0) {
870 		cmn_err(CE_WARN, "can't open objset %llu, error %d",
871 		    (unsigned long long)ds->ds_object, error);
872 		return (0);
873 	}
874 
875 	zilog = dmu_objset_zil(os);
876 	bp = (blkptr_t *)&zilog->zl_header->zh_log;
877 
878 	if (!BP_IS_HOLE(bp)) {
879 		vdev_t *vd;
880 		boolean_t valid = B_TRUE;
881 
882 		/*
883 		 * Check the first block and determine if it's on a log device
884 		 * which may have been removed or faulted prior to loading this
885 		 * pool.  If so, there's no point in checking the rest of the
886 		 * log as its content should have already been synced to the
887 		 * pool.
888 		 */
889 		spa_config_enter(os->os_spa, SCL_STATE, FTAG, RW_READER);
890 		vd = vdev_lookup_top(os->os_spa, DVA_GET_VDEV(&bp->blk_dva[0]));
891 		if (vd->vdev_islog && vdev_is_dead(vd))
892 			valid = vdev_log_state_valid(vd);
893 		spa_config_exit(os->os_spa, SCL_STATE, FTAG);
894 
895 		if (!valid)
896 			return (0);
897 
898 		/*
899 		 * Check whether the current uberblock is checkpointed (e.g.
900 		 * we are rewinding) and whether the current header has been
901 		 * claimed or not. If it hasn't then skip verifying it. We
902 		 * do this because its ZIL blocks may be part of the pool's
903 		 * state before the rewind, which is no longer valid.
904 		 */
905 		zil_header_t *zh = zil_header_in_syncing_context(zilog);
906 		if (zilog->zl_spa->spa_uberblock.ub_checkpoint_txg != 0 &&
907 		    zh->zh_claim_txg == 0)
908 			return (0);
909 	}
910 
911 	/*
912 	 * Because tx == NULL, zil_claim_log_block() will not actually claim
913 	 * any blocks, but just determine whether it is possible to do so.
914 	 * In addition to checking the log chain, zil_claim_log_block()
915 	 * will invoke zio_claim() with a done func of spa_claim_notify(),
916 	 * which will update spa_max_claim_txg.  See spa_load() for details.
917 	 */
918 	error = zil_parse(zilog, zil_claim_log_block, zil_claim_log_record, tx,
919 	    zilog->zl_header->zh_claim_txg ? -1ULL :
920 	    spa_min_claim_txg(os->os_spa));
921 
922 	return ((error == ECKSUM || error == ENOENT) ? 0 : error);
923 }
924 
925 /*
926  * When an itx is "skipped", this function is used to properly mark the
927  * waiter as "done, and signal any thread(s) waiting on it. An itx can
928  * be skipped (and not committed to an lwb) for a variety of reasons,
929  * one of them being that the itx was committed via spa_sync(), prior to
930  * it being committed to an lwb; this can happen if a thread calling
931  * zil_commit() is racing with spa_sync().
932  */
933 static void
934 zil_commit_waiter_skip(zil_commit_waiter_t *zcw)
935 {
936 	mutex_enter(&zcw->zcw_lock);
937 	ASSERT3B(zcw->zcw_done, ==, B_FALSE);
938 	zcw->zcw_done = B_TRUE;
939 	cv_broadcast(&zcw->zcw_cv);
940 	mutex_exit(&zcw->zcw_lock);
941 }
942 
943 /*
944  * This function is used when the given waiter is to be linked into an
945  * lwb's "lwb_waiter" list; i.e. when the itx is committed to the lwb.
946  * At this point, the waiter will no longer be referenced by the itx,
947  * and instead, will be referenced by the lwb.
948  */
949 static void
950 zil_commit_waiter_link_lwb(zil_commit_waiter_t *zcw, lwb_t *lwb)
951 {
952 	/*
953 	 * The lwb_waiters field of the lwb is protected by the zilog's
954 	 * zl_lock, thus it must be held when calling this function.
955 	 */
956 	ASSERT(MUTEX_HELD(&lwb->lwb_zilog->zl_lock));
957 
958 	mutex_enter(&zcw->zcw_lock);
959 	ASSERT(!list_link_active(&zcw->zcw_node));
960 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
961 	ASSERT3P(lwb, !=, NULL);
962 	ASSERT(lwb->lwb_state == LWB_STATE_OPENED ||
963 	    lwb->lwb_state == LWB_STATE_ISSUED);
964 
965 	list_insert_tail(&lwb->lwb_waiters, zcw);
966 	zcw->zcw_lwb = lwb;
967 	mutex_exit(&zcw->zcw_lock);
968 }
969 
970 /*
971  * This function is used when zio_alloc_zil() fails to allocate a ZIL
972  * block, and the given waiter must be linked to the "nolwb waiters"
973  * list inside of zil_process_commit_list().
974  */
975 static void
976 zil_commit_waiter_link_nolwb(zil_commit_waiter_t *zcw, list_t *nolwb)
977 {
978 	mutex_enter(&zcw->zcw_lock);
979 	ASSERT(!list_link_active(&zcw->zcw_node));
980 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
981 	list_insert_tail(nolwb, zcw);
982 	mutex_exit(&zcw->zcw_lock);
983 }
984 
985 void
986 zil_lwb_add_block(lwb_t *lwb, const blkptr_t *bp)
987 {
988 	avl_tree_t *t = &lwb->lwb_vdev_tree;
989 	avl_index_t where;
990 	zil_vdev_node_t *zv, zvsearch;
991 	int ndvas = BP_GET_NDVAS(bp);
992 	int i;
993 
994 	if (zfs_nocacheflush)
995 		return;
996 
997 	mutex_enter(&lwb->lwb_vdev_lock);
998 	for (i = 0; i < ndvas; i++) {
999 		zvsearch.zv_vdev = DVA_GET_VDEV(&bp->blk_dva[i]);
1000 		if (avl_find(t, &zvsearch, &where) == NULL) {
1001 			zv = kmem_alloc(sizeof (*zv), KM_SLEEP);
1002 			zv->zv_vdev = zvsearch.zv_vdev;
1003 			avl_insert(t, zv, where);
1004 		}
1005 	}
1006 	mutex_exit(&lwb->lwb_vdev_lock);
1007 }
1008 
1009 void
1010 zil_lwb_add_txg(lwb_t *lwb, uint64_t txg)
1011 {
1012 	lwb->lwb_max_txg = MAX(lwb->lwb_max_txg, txg);
1013 }
1014 
1015 /*
1016  * This function is a called after all VDEVs associated with a given lwb
1017  * write have completed their DKIOCFLUSHWRITECACHE command; or as soon
1018  * as the lwb write completes, if "zfs_nocacheflush" is set.
1019  *
1020  * The intention is for this function to be called as soon as the
1021  * contents of an lwb are considered "stable" on disk, and will survive
1022  * any sudden loss of power. At this point, any threads waiting for the
1023  * lwb to reach this state are signalled, and the "waiter" structures
1024  * are marked "done".
1025  */
1026 static void
1027 zil_lwb_flush_vdevs_done(zio_t *zio)
1028 {
1029 	lwb_t *lwb = zio->io_private;
1030 	zilog_t *zilog = lwb->lwb_zilog;
1031 	dmu_tx_t *tx = lwb->lwb_tx;
1032 	zil_commit_waiter_t *zcw;
1033 
1034 	spa_config_exit(zilog->zl_spa, SCL_STATE, lwb);
1035 
1036 	zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
1037 
1038 	mutex_enter(&zilog->zl_lock);
1039 
1040 	/*
1041 	 * Ensure the lwb buffer pointer is cleared before releasing the
1042 	 * txg. If we have had an allocation failure and the txg is
1043 	 * waiting to sync then we want zil_sync() to remove the lwb so
1044 	 * that it's not picked up as the next new one in
1045 	 * zil_process_commit_list(). zil_sync() will only remove the
1046 	 * lwb if lwb_buf is null.
1047 	 */
1048 	lwb->lwb_buf = NULL;
1049 	lwb->lwb_tx = NULL;
1050 
1051 	ASSERT3U(lwb->lwb_issued_timestamp, >, 0);
1052 	zilog->zl_last_lwb_latency = gethrtime() - lwb->lwb_issued_timestamp;
1053 
1054 	lwb->lwb_root_zio = NULL;
1055 	lwb->lwb_state = LWB_STATE_DONE;
1056 
1057 	if (zilog->zl_last_lwb_opened == lwb) {
1058 		/*
1059 		 * Remember the highest committed log sequence number
1060 		 * for ztest. We only update this value when all the log
1061 		 * writes succeeded, because ztest wants to ASSERT that
1062 		 * it got the whole log chain.
1063 		 */
1064 		zilog->zl_commit_lr_seq = zilog->zl_lr_seq;
1065 	}
1066 
1067 	while ((zcw = list_head(&lwb->lwb_waiters)) != NULL) {
1068 		mutex_enter(&zcw->zcw_lock);
1069 
1070 		ASSERT(list_link_active(&zcw->zcw_node));
1071 		list_remove(&lwb->lwb_waiters, zcw);
1072 
1073 		ASSERT3P(zcw->zcw_lwb, ==, lwb);
1074 		zcw->zcw_lwb = NULL;
1075 
1076 		zcw->zcw_zio_error = zio->io_error;
1077 
1078 		ASSERT3B(zcw->zcw_done, ==, B_FALSE);
1079 		zcw->zcw_done = B_TRUE;
1080 		cv_broadcast(&zcw->zcw_cv);
1081 
1082 		mutex_exit(&zcw->zcw_lock);
1083 	}
1084 
1085 	mutex_exit(&zilog->zl_lock);
1086 
1087 	/*
1088 	 * Now that we've written this log block, we have a stable pointer
1089 	 * to the next block in the chain, so it's OK to let the txg in
1090 	 * which we allocated the next block sync.
1091 	 */
1092 	dmu_tx_commit(tx);
1093 }
1094 
1095 /*
1096  * This is called when an lwb write completes. This means, this specific
1097  * lwb was written to disk, and all dependent lwb have also been
1098  * written to disk.
1099  *
1100  * At this point, a DKIOCFLUSHWRITECACHE command hasn't been issued to
1101  * the VDEVs involved in writing out this specific lwb. The lwb will be
1102  * "done" once zil_lwb_flush_vdevs_done() is called, which occurs in the
1103  * zio completion callback for the lwb's root zio.
1104  */
1105 static void
1106 zil_lwb_write_done(zio_t *zio)
1107 {
1108 	lwb_t *lwb = zio->io_private;
1109 	spa_t *spa = zio->io_spa;
1110 	zilog_t *zilog = lwb->lwb_zilog;
1111 	avl_tree_t *t = &lwb->lwb_vdev_tree;
1112 	void *cookie = NULL;
1113 	zil_vdev_node_t *zv;
1114 
1115 	ASSERT3S(spa_config_held(spa, SCL_STATE, RW_READER), !=, 0);
1116 
1117 	ASSERT(BP_GET_COMPRESS(zio->io_bp) == ZIO_COMPRESS_OFF);
1118 	ASSERT(BP_GET_TYPE(zio->io_bp) == DMU_OT_INTENT_LOG);
1119 	ASSERT(BP_GET_LEVEL(zio->io_bp) == 0);
1120 	ASSERT(BP_GET_BYTEORDER(zio->io_bp) == ZFS_HOST_BYTEORDER);
1121 	ASSERT(!BP_IS_GANG(zio->io_bp));
1122 	ASSERT(!BP_IS_HOLE(zio->io_bp));
1123 	ASSERT(BP_GET_FILL(zio->io_bp) == 0);
1124 
1125 	abd_put(zio->io_abd);
1126 
1127 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_ISSUED);
1128 
1129 	mutex_enter(&zilog->zl_lock);
1130 	lwb->lwb_write_zio = NULL;
1131 	mutex_exit(&zilog->zl_lock);
1132 
1133 	if (avl_numnodes(t) == 0)
1134 		return;
1135 
1136 	/*
1137 	 * If there was an IO error, we're not going to call zio_flush()
1138 	 * on these vdevs, so we simply empty the tree and free the
1139 	 * nodes. We avoid calling zio_flush() since there isn't any
1140 	 * good reason for doing so, after the lwb block failed to be
1141 	 * written out.
1142 	 */
1143 	if (zio->io_error != 0) {
1144 		while ((zv = avl_destroy_nodes(t, &cookie)) != NULL)
1145 			kmem_free(zv, sizeof (*zv));
1146 		return;
1147 	}
1148 
1149 	while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
1150 		vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
1151 		if (vd != NULL)
1152 			zio_flush(lwb->lwb_root_zio, vd);
1153 		kmem_free(zv, sizeof (*zv));
1154 	}
1155 }
1156 
1157 /*
1158  * This function's purpose is to "open" an lwb such that it is ready to
1159  * accept new itxs being committed to it. To do this, the lwb's zio
1160  * structures are created, and linked to the lwb. This function is
1161  * idempotent; if the passed in lwb has already been opened, this
1162  * function is essentially a no-op.
1163  */
1164 static void
1165 zil_lwb_write_open(zilog_t *zilog, lwb_t *lwb)
1166 {
1167 	zbookmark_phys_t zb;
1168 	zio_priority_t prio;
1169 
1170 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1171 	ASSERT3P(lwb, !=, NULL);
1172 	EQUIV(lwb->lwb_root_zio == NULL, lwb->lwb_state == LWB_STATE_CLOSED);
1173 	EQUIV(lwb->lwb_root_zio != NULL, lwb->lwb_state == LWB_STATE_OPENED);
1174 
1175 	SET_BOOKMARK(&zb, lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_OBJSET],
1176 	    ZB_ZIL_OBJECT, ZB_ZIL_LEVEL,
1177 	    lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_SEQ]);
1178 
1179 	if (lwb->lwb_root_zio == NULL) {
1180 		abd_t *lwb_abd = abd_get_from_buf(lwb->lwb_buf,
1181 		    BP_GET_LSIZE(&lwb->lwb_blk));
1182 
1183 		if (!lwb->lwb_slog || zilog->zl_cur_used <= zil_slog_bulk)
1184 			prio = ZIO_PRIORITY_SYNC_WRITE;
1185 		else
1186 			prio = ZIO_PRIORITY_ASYNC_WRITE;
1187 
1188 		lwb->lwb_root_zio = zio_root(zilog->zl_spa,
1189 		    zil_lwb_flush_vdevs_done, lwb, ZIO_FLAG_CANFAIL);
1190 		ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1191 
1192 		lwb->lwb_write_zio = zio_rewrite(lwb->lwb_root_zio,
1193 		    zilog->zl_spa, 0, &lwb->lwb_blk, lwb_abd,
1194 		    BP_GET_LSIZE(&lwb->lwb_blk), zil_lwb_write_done, lwb,
1195 		    prio, ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE, &zb);
1196 		ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1197 
1198 		lwb->lwb_state = LWB_STATE_OPENED;
1199 
1200 		mutex_enter(&zilog->zl_lock);
1201 
1202 		/*
1203 		 * The zilog's "zl_last_lwb_opened" field is used to
1204 		 * build the lwb/zio dependency chain, which is used to
1205 		 * preserve the ordering of lwb completions that is
1206 		 * required by the semantics of the ZIL. Each new lwb
1207 		 * zio becomes a parent of the "previous" lwb zio, such
1208 		 * that the new lwb's zio cannot complete until the
1209 		 * "previous" lwb's zio completes.
1210 		 *
1211 		 * This is required by the semantics of zil_commit();
1212 		 * the commit waiters attached to the lwbs will be woken
1213 		 * in the lwb zio's completion callback, so this zio
1214 		 * dependency graph ensures the waiters are woken in the
1215 		 * correct order (the same order the lwbs were created).
1216 		 */
1217 		lwb_t *last_lwb_opened = zilog->zl_last_lwb_opened;
1218 		if (last_lwb_opened != NULL &&
1219 		    last_lwb_opened->lwb_state != LWB_STATE_DONE) {
1220 			ASSERT(last_lwb_opened->lwb_state == LWB_STATE_OPENED ||
1221 			    last_lwb_opened->lwb_state == LWB_STATE_ISSUED);
1222 			ASSERT3P(last_lwb_opened->lwb_root_zio, !=, NULL);
1223 			zio_add_child(lwb->lwb_root_zio,
1224 			    last_lwb_opened->lwb_root_zio);
1225 		}
1226 		zilog->zl_last_lwb_opened = lwb;
1227 
1228 		mutex_exit(&zilog->zl_lock);
1229 	}
1230 
1231 	ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1232 	ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1233 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
1234 }
1235 
1236 /*
1237  * Define a limited set of intent log block sizes.
1238  *
1239  * These must be a multiple of 4KB. Note only the amount used (again
1240  * aligned to 4KB) actually gets written. However, we can't always just
1241  * allocate SPA_OLD_MAXBLOCKSIZE as the slog space could be exhausted.
1242  */
1243 uint64_t zil_block_buckets[] = {
1244     4096,		/* non TX_WRITE */
1245     8192+4096,		/* data base */
1246     32*1024 + 4096, 	/* NFS writes */
1247     UINT64_MAX
1248 };
1249 
1250 /*
1251  * Start a log block write and advance to the next log block.
1252  * Calls are serialized.
1253  */
1254 static lwb_t *
1255 zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
1256 {
1257 	lwb_t *nlwb = NULL;
1258 	zil_chain_t *zilc;
1259 	spa_t *spa = zilog->zl_spa;
1260 	blkptr_t *bp;
1261 	dmu_tx_t *tx;
1262 	uint64_t txg;
1263 	uint64_t zil_blksz, wsz;
1264 	int i, error;
1265 	boolean_t slog;
1266 
1267 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1268 	ASSERT3P(lwb->lwb_root_zio, !=, NULL);
1269 	ASSERT3P(lwb->lwb_write_zio, !=, NULL);
1270 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
1271 
1272 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
1273 		zilc = (zil_chain_t *)lwb->lwb_buf;
1274 		bp = &zilc->zc_next_blk;
1275 	} else {
1276 		zilc = (zil_chain_t *)(lwb->lwb_buf + lwb->lwb_sz);
1277 		bp = &zilc->zc_next_blk;
1278 	}
1279 
1280 	ASSERT(lwb->lwb_nused <= lwb->lwb_sz);
1281 
1282 	/*
1283 	 * Allocate the next block and save its address in this block
1284 	 * before writing it in order to establish the log chain.
1285 	 * Note that if the allocation of nlwb synced before we wrote
1286 	 * the block that points at it (lwb), we'd leak it if we crashed.
1287 	 * Therefore, we don't do dmu_tx_commit() until zil_lwb_write_done().
1288 	 * We dirty the dataset to ensure that zil_sync() will be called
1289 	 * to clean up in the event of allocation failure or I/O failure.
1290 	 */
1291 
1292 	tx = dmu_tx_create(zilog->zl_os);
1293 
1294 	/*
1295 	 * Since we are not going to create any new dirty data, and we
1296 	 * can even help with clearing the existing dirty data, we
1297 	 * should not be subject to the dirty data based delays. We
1298 	 * use TXG_NOTHROTTLE to bypass the delay mechanism.
1299 	 */
1300 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT | TXG_NOTHROTTLE));
1301 
1302 	dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
1303 	txg = dmu_tx_get_txg(tx);
1304 
1305 	lwb->lwb_tx = tx;
1306 
1307 	/*
1308 	 * Log blocks are pre-allocated. Here we select the size of the next
1309 	 * block, based on size used in the last block.
1310 	 * - first find the smallest bucket that will fit the block from a
1311 	 *   limited set of block sizes. This is because it's faster to write
1312 	 *   blocks allocated from the same metaslab as they are adjacent or
1313 	 *   close.
1314 	 * - next find the maximum from the new suggested size and an array of
1315 	 *   previous sizes. This lessens a picket fence effect of wrongly
1316 	 *   guesssing the size if we have a stream of say 2k, 64k, 2k, 64k
1317 	 *   requests.
1318 	 *
1319 	 * Note we only write what is used, but we can't just allocate
1320 	 * the maximum block size because we can exhaust the available
1321 	 * pool log space.
1322 	 */
1323 	zil_blksz = zilog->zl_cur_used + sizeof (zil_chain_t);
1324 	for (i = 0; zil_blksz > zil_block_buckets[i]; i++)
1325 		continue;
1326 	zil_blksz = zil_block_buckets[i];
1327 	if (zil_blksz == UINT64_MAX)
1328 		zil_blksz = SPA_OLD_MAXBLOCKSIZE;
1329 	zilog->zl_prev_blks[zilog->zl_prev_rotor] = zil_blksz;
1330 	for (i = 0; i < ZIL_PREV_BLKS; i++)
1331 		zil_blksz = MAX(zil_blksz, zilog->zl_prev_blks[i]);
1332 	zilog->zl_prev_rotor = (zilog->zl_prev_rotor + 1) & (ZIL_PREV_BLKS - 1);
1333 
1334 	BP_ZERO(bp);
1335 
1336 	/* pass the old blkptr in order to spread log blocks across devs */
1337 	error = zio_alloc_zil(spa, zilog->zl_os->os_dsl_dataset->ds_object,
1338 	    txg, bp, &lwb->lwb_blk, zil_blksz, &slog);
1339 	if (error == 0) {
1340 		ASSERT3U(bp->blk_birth, ==, txg);
1341 		bp->blk_cksum = lwb->lwb_blk.blk_cksum;
1342 		bp->blk_cksum.zc_word[ZIL_ZC_SEQ]++;
1343 
1344 		/*
1345 		 * Allocate a new log write block (lwb).
1346 		 */
1347 		nlwb = zil_alloc_lwb(zilog, bp, slog, txg);
1348 	}
1349 
1350 	if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
1351 		/* For Slim ZIL only write what is used. */
1352 		wsz = P2ROUNDUP_TYPED(lwb->lwb_nused, ZIL_MIN_BLKSZ, uint64_t);
1353 		ASSERT3U(wsz, <=, lwb->lwb_sz);
1354 		zio_shrink(lwb->lwb_write_zio, wsz);
1355 
1356 	} else {
1357 		wsz = lwb->lwb_sz;
1358 	}
1359 
1360 	zilc->zc_pad = 0;
1361 	zilc->zc_nused = lwb->lwb_nused;
1362 	zilc->zc_eck.zec_cksum = lwb->lwb_blk.blk_cksum;
1363 
1364 	/*
1365 	 * clear unused data for security
1366 	 */
1367 	bzero(lwb->lwb_buf + lwb->lwb_nused, wsz - lwb->lwb_nused);
1368 
1369 	spa_config_enter(zilog->zl_spa, SCL_STATE, lwb, RW_READER);
1370 
1371 	zil_lwb_add_block(lwb, &lwb->lwb_blk);
1372 	lwb->lwb_issued_timestamp = gethrtime();
1373 	lwb->lwb_state = LWB_STATE_ISSUED;
1374 
1375 	zio_nowait(lwb->lwb_root_zio);
1376 	zio_nowait(lwb->lwb_write_zio);
1377 
1378 	/*
1379 	 * If there was an allocation failure then nlwb will be null which
1380 	 * forces a txg_wait_synced().
1381 	 */
1382 	return (nlwb);
1383 }
1384 
1385 static lwb_t *
1386 zil_lwb_commit(zilog_t *zilog, itx_t *itx, lwb_t *lwb)
1387 {
1388 	lr_t *lrcb, *lrc;
1389 	lr_write_t *lrwb, *lrw;
1390 	char *lr_buf;
1391 	uint64_t dlen, dnow, lwb_sp, reclen, txg;
1392 
1393 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1394 	ASSERT3P(lwb, !=, NULL);
1395 	ASSERT3P(lwb->lwb_buf, !=, NULL);
1396 
1397 	zil_lwb_write_open(zilog, lwb);
1398 
1399 	lrc = &itx->itx_lr;
1400 	lrw = (lr_write_t *)lrc;
1401 
1402 	/*
1403 	 * A commit itx doesn't represent any on-disk state; instead
1404 	 * it's simply used as a place holder on the commit list, and
1405 	 * provides a mechanism for attaching a "commit waiter" onto the
1406 	 * correct lwb (such that the waiter can be signalled upon
1407 	 * completion of that lwb). Thus, we don't process this itx's
1408 	 * log record if it's a commit itx (these itx's don't have log
1409 	 * records), and instead link the itx's waiter onto the lwb's
1410 	 * list of waiters.
1411 	 *
1412 	 * For more details, see the comment above zil_commit().
1413 	 */
1414 	if (lrc->lrc_txtype == TX_COMMIT) {
1415 		mutex_enter(&zilog->zl_lock);
1416 		zil_commit_waiter_link_lwb(itx->itx_private, lwb);
1417 		itx->itx_private = NULL;
1418 		mutex_exit(&zilog->zl_lock);
1419 		return (lwb);
1420 	}
1421 
1422 	if (lrc->lrc_txtype == TX_WRITE && itx->itx_wr_state == WR_NEED_COPY) {
1423 		dlen = P2ROUNDUP_TYPED(
1424 		    lrw->lr_length, sizeof (uint64_t), uint64_t);
1425 	} else {
1426 		dlen = 0;
1427 	}
1428 	reclen = lrc->lrc_reclen;
1429 	zilog->zl_cur_used += (reclen + dlen);
1430 	txg = lrc->lrc_txg;
1431 
1432 	ASSERT3U(zilog->zl_cur_used, <, UINT64_MAX - (reclen + dlen));
1433 
1434 cont:
1435 	/*
1436 	 * If this record won't fit in the current log block, start a new one.
1437 	 * For WR_NEED_COPY optimize layout for minimal number of chunks.
1438 	 */
1439 	lwb_sp = lwb->lwb_sz - lwb->lwb_nused;
1440 	if (reclen > lwb_sp || (reclen + dlen > lwb_sp &&
1441 	    lwb_sp < ZIL_MAX_WASTE_SPACE && (dlen % ZIL_MAX_LOG_DATA == 0 ||
1442 	    lwb_sp < reclen + dlen % ZIL_MAX_LOG_DATA))) {
1443 		lwb = zil_lwb_write_issue(zilog, lwb);
1444 		if (lwb == NULL)
1445 			return (NULL);
1446 		zil_lwb_write_open(zilog, lwb);
1447 		ASSERT(LWB_EMPTY(lwb));
1448 		lwb_sp = lwb->lwb_sz - lwb->lwb_nused;
1449 		ASSERT3U(reclen + MIN(dlen, sizeof (uint64_t)), <=, lwb_sp);
1450 	}
1451 
1452 	dnow = MIN(dlen, lwb_sp - reclen);
1453 	lr_buf = lwb->lwb_buf + lwb->lwb_nused;
1454 	bcopy(lrc, lr_buf, reclen);
1455 	lrcb = (lr_t *)lr_buf;		/* Like lrc, but inside lwb. */
1456 	lrwb = (lr_write_t *)lrcb;	/* Like lrw, but inside lwb. */
1457 
1458 	/*
1459 	 * If it's a write, fetch the data or get its blkptr as appropriate.
1460 	 */
1461 	if (lrc->lrc_txtype == TX_WRITE) {
1462 		if (txg > spa_freeze_txg(zilog->zl_spa))
1463 			txg_wait_synced(zilog->zl_dmu_pool, txg);
1464 		if (itx->itx_wr_state != WR_COPIED) {
1465 			char *dbuf;
1466 			int error;
1467 
1468 			if (itx->itx_wr_state == WR_NEED_COPY) {
1469 				dbuf = lr_buf + reclen;
1470 				lrcb->lrc_reclen += dnow;
1471 				if (lrwb->lr_length > dnow)
1472 					lrwb->lr_length = dnow;
1473 				lrw->lr_offset += dnow;
1474 				lrw->lr_length -= dnow;
1475 			} else {
1476 				ASSERT(itx->itx_wr_state == WR_INDIRECT);
1477 				dbuf = NULL;
1478 			}
1479 
1480 			/*
1481 			 * We pass in the "lwb_write_zio" rather than
1482 			 * "lwb_root_zio" so that the "lwb_write_zio"
1483 			 * becomes the parent of any zio's created by
1484 			 * the "zl_get_data" callback. The vdevs are
1485 			 * flushed after the "lwb_write_zio" completes,
1486 			 * so we want to make sure that completion
1487 			 * callback waits for these additional zio's,
1488 			 * such that the vdevs used by those zio's will
1489 			 * be included in the lwb's vdev tree, and those
1490 			 * vdevs will be properly flushed. If we passed
1491 			 * in "lwb_root_zio" here, then these additional
1492 			 * vdevs may not be flushed; e.g. if these zio's
1493 			 * completed after "lwb_write_zio" completed.
1494 			 */
1495 			error = zilog->zl_get_data(itx->itx_private,
1496 			    lrwb, dbuf, lwb, lwb->lwb_write_zio);
1497 
1498 			if (error == EIO) {
1499 				txg_wait_synced(zilog->zl_dmu_pool, txg);
1500 				return (lwb);
1501 			}
1502 			if (error != 0) {
1503 				ASSERT(error == ENOENT || error == EEXIST ||
1504 				    error == EALREADY);
1505 				return (lwb);
1506 			}
1507 		}
1508 	}
1509 
1510 	/*
1511 	 * We're actually making an entry, so update lrc_seq to be the
1512 	 * log record sequence number.  Note that this is generally not
1513 	 * equal to the itx sequence number because not all transactions
1514 	 * are synchronous, and sometimes spa_sync() gets there first.
1515 	 */
1516 	lrcb->lrc_seq = ++zilog->zl_lr_seq;
1517 	lwb->lwb_nused += reclen + dnow;
1518 
1519 	zil_lwb_add_txg(lwb, txg);
1520 
1521 	ASSERT3U(lwb->lwb_nused, <=, lwb->lwb_sz);
1522 	ASSERT0(P2PHASE(lwb->lwb_nused, sizeof (uint64_t)));
1523 
1524 	dlen -= dnow;
1525 	if (dlen > 0) {
1526 		zilog->zl_cur_used += reclen;
1527 		goto cont;
1528 	}
1529 
1530 	return (lwb);
1531 }
1532 
1533 itx_t *
1534 zil_itx_create(uint64_t txtype, size_t lrsize)
1535 {
1536 	itx_t *itx;
1537 
1538 	lrsize = P2ROUNDUP_TYPED(lrsize, sizeof (uint64_t), size_t);
1539 
1540 	itx = kmem_alloc(offsetof(itx_t, itx_lr) + lrsize, KM_SLEEP);
1541 	itx->itx_lr.lrc_txtype = txtype;
1542 	itx->itx_lr.lrc_reclen = lrsize;
1543 	itx->itx_lr.lrc_seq = 0;	/* defensive */
1544 	itx->itx_sync = B_TRUE;		/* default is synchronous */
1545 
1546 	return (itx);
1547 }
1548 
1549 void
1550 zil_itx_destroy(itx_t *itx)
1551 {
1552 	kmem_free(itx, offsetof(itx_t, itx_lr) + itx->itx_lr.lrc_reclen);
1553 }
1554 
1555 /*
1556  * Free up the sync and async itxs. The itxs_t has already been detached
1557  * so no locks are needed.
1558  */
1559 static void
1560 zil_itxg_clean(itxs_t *itxs)
1561 {
1562 	itx_t *itx;
1563 	list_t *list;
1564 	avl_tree_t *t;
1565 	void *cookie;
1566 	itx_async_node_t *ian;
1567 
1568 	list = &itxs->i_sync_list;
1569 	while ((itx = list_head(list)) != NULL) {
1570 		/*
1571 		 * In the general case, commit itxs will not be found
1572 		 * here, as they'll be committed to an lwb via
1573 		 * zil_lwb_commit(), and free'd in that function. Having
1574 		 * said that, it is still possible for commit itxs to be
1575 		 * found here, due to the following race:
1576 		 *
1577 		 *	- a thread calls zil_commit() which assigns the
1578 		 *	  commit itx to a per-txg i_sync_list
1579 		 *	- zil_itxg_clean() is called (e.g. via spa_sync())
1580 		 *	  while the waiter is still on the i_sync_list
1581 		 *
1582 		 * There's nothing to prevent syncing the txg while the
1583 		 * waiter is on the i_sync_list. This normally doesn't
1584 		 * happen because spa_sync() is slower than zil_commit(),
1585 		 * but if zil_commit() calls txg_wait_synced() (e.g.
1586 		 * because zil_create() or zil_commit_writer_stall() is
1587 		 * called) we will hit this case.
1588 		 */
1589 		if (itx->itx_lr.lrc_txtype == TX_COMMIT)
1590 			zil_commit_waiter_skip(itx->itx_private);
1591 
1592 		list_remove(list, itx);
1593 		zil_itx_destroy(itx);
1594 	}
1595 
1596 	cookie = NULL;
1597 	t = &itxs->i_async_tree;
1598 	while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
1599 		list = &ian->ia_list;
1600 		while ((itx = list_head(list)) != NULL) {
1601 			list_remove(list, itx);
1602 			/* commit itxs should never be on the async lists. */
1603 			ASSERT3U(itx->itx_lr.lrc_txtype, !=, TX_COMMIT);
1604 			zil_itx_destroy(itx);
1605 		}
1606 		list_destroy(list);
1607 		kmem_free(ian, sizeof (itx_async_node_t));
1608 	}
1609 	avl_destroy(t);
1610 
1611 	kmem_free(itxs, sizeof (itxs_t));
1612 }
1613 
1614 static int
1615 zil_aitx_compare(const void *x1, const void *x2)
1616 {
1617 	const uint64_t o1 = ((itx_async_node_t *)x1)->ia_foid;
1618 	const uint64_t o2 = ((itx_async_node_t *)x2)->ia_foid;
1619 
1620 	if (o1 < o2)
1621 		return (-1);
1622 	if (o1 > o2)
1623 		return (1);
1624 
1625 	return (0);
1626 }
1627 
1628 /*
1629  * Remove all async itx with the given oid.
1630  */
1631 static void
1632 zil_remove_async(zilog_t *zilog, uint64_t oid)
1633 {
1634 	uint64_t otxg, txg;
1635 	itx_async_node_t *ian;
1636 	avl_tree_t *t;
1637 	avl_index_t where;
1638 	list_t clean_list;
1639 	itx_t *itx;
1640 
1641 	ASSERT(oid != 0);
1642 	list_create(&clean_list, sizeof (itx_t), offsetof(itx_t, itx_node));
1643 
1644 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1645 		otxg = ZILTEST_TXG;
1646 	else
1647 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1648 
1649 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1650 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1651 
1652 		mutex_enter(&itxg->itxg_lock);
1653 		if (itxg->itxg_txg != txg) {
1654 			mutex_exit(&itxg->itxg_lock);
1655 			continue;
1656 		}
1657 
1658 		/*
1659 		 * Locate the object node and append its list.
1660 		 */
1661 		t = &itxg->itxg_itxs->i_async_tree;
1662 		ian = avl_find(t, &oid, &where);
1663 		if (ian != NULL)
1664 			list_move_tail(&clean_list, &ian->ia_list);
1665 		mutex_exit(&itxg->itxg_lock);
1666 	}
1667 	while ((itx = list_head(&clean_list)) != NULL) {
1668 		list_remove(&clean_list, itx);
1669 		/* commit itxs should never be on the async lists. */
1670 		ASSERT3U(itx->itx_lr.lrc_txtype, !=, TX_COMMIT);
1671 		zil_itx_destroy(itx);
1672 	}
1673 	list_destroy(&clean_list);
1674 }
1675 
1676 void
1677 zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx)
1678 {
1679 	uint64_t txg;
1680 	itxg_t *itxg;
1681 	itxs_t *itxs, *clean = NULL;
1682 
1683 	/*
1684 	 * Object ids can be re-instantiated in the next txg so
1685 	 * remove any async transactions to avoid future leaks.
1686 	 * This can happen if a fsync occurs on the re-instantiated
1687 	 * object for a WR_INDIRECT or WR_NEED_COPY write, which gets
1688 	 * the new file data and flushes a write record for the old object.
1689 	 */
1690 	if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_REMOVE)
1691 		zil_remove_async(zilog, itx->itx_oid);
1692 
1693 	/*
1694 	 * Ensure the data of a renamed file is committed before the rename.
1695 	 */
1696 	if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_RENAME)
1697 		zil_async_to_sync(zilog, itx->itx_oid);
1698 
1699 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX)
1700 		txg = ZILTEST_TXG;
1701 	else
1702 		txg = dmu_tx_get_txg(tx);
1703 
1704 	itxg = &zilog->zl_itxg[txg & TXG_MASK];
1705 	mutex_enter(&itxg->itxg_lock);
1706 	itxs = itxg->itxg_itxs;
1707 	if (itxg->itxg_txg != txg) {
1708 		if (itxs != NULL) {
1709 			/*
1710 			 * The zil_clean callback hasn't got around to cleaning
1711 			 * this itxg. Save the itxs for release below.
1712 			 * This should be rare.
1713 			 */
1714 			zfs_dbgmsg("zil_itx_assign: missed itx cleanup for "
1715 			    "txg %llu", itxg->itxg_txg);
1716 			clean = itxg->itxg_itxs;
1717 		}
1718 		itxg->itxg_txg = txg;
1719 		itxs = itxg->itxg_itxs = kmem_zalloc(sizeof (itxs_t), KM_SLEEP);
1720 
1721 		list_create(&itxs->i_sync_list, sizeof (itx_t),
1722 		    offsetof(itx_t, itx_node));
1723 		avl_create(&itxs->i_async_tree, zil_aitx_compare,
1724 		    sizeof (itx_async_node_t),
1725 		    offsetof(itx_async_node_t, ia_node));
1726 	}
1727 	if (itx->itx_sync) {
1728 		list_insert_tail(&itxs->i_sync_list, itx);
1729 	} else {
1730 		avl_tree_t *t = &itxs->i_async_tree;
1731 		uint64_t foid = ((lr_ooo_t *)&itx->itx_lr)->lr_foid;
1732 		itx_async_node_t *ian;
1733 		avl_index_t where;
1734 
1735 		ian = avl_find(t, &foid, &where);
1736 		if (ian == NULL) {
1737 			ian = kmem_alloc(sizeof (itx_async_node_t), KM_SLEEP);
1738 			list_create(&ian->ia_list, sizeof (itx_t),
1739 			    offsetof(itx_t, itx_node));
1740 			ian->ia_foid = foid;
1741 			avl_insert(t, ian, where);
1742 		}
1743 		list_insert_tail(&ian->ia_list, itx);
1744 	}
1745 
1746 	itx->itx_lr.lrc_txg = dmu_tx_get_txg(tx);
1747 
1748 	/*
1749 	 * We don't want to dirty the ZIL using ZILTEST_TXG, because
1750 	 * zil_clean() will never be called using ZILTEST_TXG. Thus, we
1751 	 * need to be careful to always dirty the ZIL using the "real"
1752 	 * TXG (not itxg_txg) even when the SPA is frozen.
1753 	 */
1754 	zilog_dirty(zilog, dmu_tx_get_txg(tx));
1755 	mutex_exit(&itxg->itxg_lock);
1756 
1757 	/* Release the old itxs now we've dropped the lock */
1758 	if (clean != NULL)
1759 		zil_itxg_clean(clean);
1760 }
1761 
1762 /*
1763  * If there are any in-memory intent log transactions which have now been
1764  * synced then start up a taskq to free them. We should only do this after we
1765  * have written out the uberblocks (i.e. txg has been comitted) so that
1766  * don't inadvertently clean out in-memory log records that would be required
1767  * by zil_commit().
1768  */
1769 void
1770 zil_clean(zilog_t *zilog, uint64_t synced_txg)
1771 {
1772 	itxg_t *itxg = &zilog->zl_itxg[synced_txg & TXG_MASK];
1773 	itxs_t *clean_me;
1774 
1775 	ASSERT3U(synced_txg, <, ZILTEST_TXG);
1776 
1777 	mutex_enter(&itxg->itxg_lock);
1778 	if (itxg->itxg_itxs == NULL || itxg->itxg_txg == ZILTEST_TXG) {
1779 		mutex_exit(&itxg->itxg_lock);
1780 		return;
1781 	}
1782 	ASSERT3U(itxg->itxg_txg, <=, synced_txg);
1783 	ASSERT3U(itxg->itxg_txg, !=, 0);
1784 	clean_me = itxg->itxg_itxs;
1785 	itxg->itxg_itxs = NULL;
1786 	itxg->itxg_txg = 0;
1787 	mutex_exit(&itxg->itxg_lock);
1788 	/*
1789 	 * Preferably start a task queue to free up the old itxs but
1790 	 * if taskq_dispatch can't allocate resources to do that then
1791 	 * free it in-line. This should be rare. Note, using TQ_SLEEP
1792 	 * created a bad performance problem.
1793 	 */
1794 	ASSERT3P(zilog->zl_dmu_pool, !=, NULL);
1795 	ASSERT3P(zilog->zl_dmu_pool->dp_zil_clean_taskq, !=, NULL);
1796 	if (taskq_dispatch(zilog->zl_dmu_pool->dp_zil_clean_taskq,
1797 	    (void (*)(void *))zil_itxg_clean, clean_me, TQ_NOSLEEP) == NULL)
1798 		zil_itxg_clean(clean_me);
1799 }
1800 
1801 /*
1802  * This function will traverse the queue of itxs that need to be
1803  * committed, and move them onto the ZIL's zl_itx_commit_list.
1804  */
1805 static void
1806 zil_get_commit_list(zilog_t *zilog)
1807 {
1808 	uint64_t otxg, txg;
1809 	list_t *commit_list = &zilog->zl_itx_commit_list;
1810 
1811 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1812 
1813 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1814 		otxg = ZILTEST_TXG;
1815 	else
1816 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1817 
1818 	/*
1819 	 * This is inherently racy, since there is nothing to prevent
1820 	 * the last synced txg from changing. That's okay since we'll
1821 	 * only commit things in the future.
1822 	 */
1823 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1824 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1825 
1826 		mutex_enter(&itxg->itxg_lock);
1827 		if (itxg->itxg_txg != txg) {
1828 			mutex_exit(&itxg->itxg_lock);
1829 			continue;
1830 		}
1831 
1832 		/*
1833 		 * If we're adding itx records to the zl_itx_commit_list,
1834 		 * then the zil better be dirty in this "txg". We can assert
1835 		 * that here since we're holding the itxg_lock which will
1836 		 * prevent spa_sync from cleaning it. Once we add the itxs
1837 		 * to the zl_itx_commit_list we must commit it to disk even
1838 		 * if it's unnecessary (i.e. the txg was synced).
1839 		 */
1840 		ASSERT(zilog_is_dirty_in_txg(zilog, txg) ||
1841 		    spa_freeze_txg(zilog->zl_spa) != UINT64_MAX);
1842 		list_move_tail(commit_list, &itxg->itxg_itxs->i_sync_list);
1843 
1844 		mutex_exit(&itxg->itxg_lock);
1845 	}
1846 }
1847 
1848 /*
1849  * Move the async itxs for a specified object to commit into sync lists.
1850  */
1851 static void
1852 zil_async_to_sync(zilog_t *zilog, uint64_t foid)
1853 {
1854 	uint64_t otxg, txg;
1855 	itx_async_node_t *ian;
1856 	avl_tree_t *t;
1857 	avl_index_t where;
1858 
1859 	if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
1860 		otxg = ZILTEST_TXG;
1861 	else
1862 		otxg = spa_last_synced_txg(zilog->zl_spa) + 1;
1863 
1864 	/*
1865 	 * This is inherently racy, since there is nothing to prevent
1866 	 * the last synced txg from changing.
1867 	 */
1868 	for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
1869 		itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];
1870 
1871 		mutex_enter(&itxg->itxg_lock);
1872 		if (itxg->itxg_txg != txg) {
1873 			mutex_exit(&itxg->itxg_lock);
1874 			continue;
1875 		}
1876 
1877 		/*
1878 		 * If a foid is specified then find that node and append its
1879 		 * list. Otherwise walk the tree appending all the lists
1880 		 * to the sync list. We add to the end rather than the
1881 		 * beginning to ensure the create has happened.
1882 		 */
1883 		t = &itxg->itxg_itxs->i_async_tree;
1884 		if (foid != 0) {
1885 			ian = avl_find(t, &foid, &where);
1886 			if (ian != NULL) {
1887 				list_move_tail(&itxg->itxg_itxs->i_sync_list,
1888 				    &ian->ia_list);
1889 			}
1890 		} else {
1891 			void *cookie = NULL;
1892 
1893 			while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
1894 				list_move_tail(&itxg->itxg_itxs->i_sync_list,
1895 				    &ian->ia_list);
1896 				list_destroy(&ian->ia_list);
1897 				kmem_free(ian, sizeof (itx_async_node_t));
1898 			}
1899 		}
1900 		mutex_exit(&itxg->itxg_lock);
1901 	}
1902 }
1903 
1904 /*
1905  * This function will prune commit itxs that are at the head of the
1906  * commit list (it won't prune past the first non-commit itx), and
1907  * either: a) attach them to the last lwb that's still pending
1908  * completion, or b) skip them altogether.
1909  *
1910  * This is used as a performance optimization to prevent commit itxs
1911  * from generating new lwbs when it's unnecessary to do so.
1912  */
1913 static void
1914 zil_prune_commit_list(zilog_t *zilog)
1915 {
1916 	itx_t *itx;
1917 
1918 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1919 
1920 	while (itx = list_head(&zilog->zl_itx_commit_list)) {
1921 		lr_t *lrc = &itx->itx_lr;
1922 		if (lrc->lrc_txtype != TX_COMMIT)
1923 			break;
1924 
1925 		mutex_enter(&zilog->zl_lock);
1926 
1927 		lwb_t *last_lwb = zilog->zl_last_lwb_opened;
1928 		if (last_lwb == NULL || last_lwb->lwb_state == LWB_STATE_DONE) {
1929 			/*
1930 			 * All of the itxs this waiter was waiting on
1931 			 * must have already completed (or there were
1932 			 * never any itx's for it to wait on), so it's
1933 			 * safe to skip this waiter and mark it done.
1934 			 */
1935 			zil_commit_waiter_skip(itx->itx_private);
1936 		} else {
1937 			zil_commit_waiter_link_lwb(itx->itx_private, last_lwb);
1938 			itx->itx_private = NULL;
1939 		}
1940 
1941 		mutex_exit(&zilog->zl_lock);
1942 
1943 		list_remove(&zilog->zl_itx_commit_list, itx);
1944 		zil_itx_destroy(itx);
1945 	}
1946 
1947 	IMPLY(itx != NULL, itx->itx_lr.lrc_txtype != TX_COMMIT);
1948 }
1949 
1950 static void
1951 zil_commit_writer_stall(zilog_t *zilog)
1952 {
1953 	/*
1954 	 * When zio_alloc_zil() fails to allocate the next lwb block on
1955 	 * disk, we must call txg_wait_synced() to ensure all of the
1956 	 * lwbs in the zilog's zl_lwb_list are synced and then freed (in
1957 	 * zil_sync()), such that any subsequent ZIL writer (i.e. a call
1958 	 * to zil_process_commit_list()) will have to call zil_create(),
1959 	 * and start a new ZIL chain.
1960 	 *
1961 	 * Since zil_alloc_zil() failed, the lwb that was previously
1962 	 * issued does not have a pointer to the "next" lwb on disk.
1963 	 * Thus, if another ZIL writer thread was to allocate the "next"
1964 	 * on-disk lwb, that block could be leaked in the event of a
1965 	 * crash (because the previous lwb on-disk would not point to
1966 	 * it).
1967 	 *
1968 	 * We must hold the zilog's zl_issuer_lock while we do this, to
1969 	 * ensure no new threads enter zil_process_commit_list() until
1970 	 * all lwb's in the zl_lwb_list have been synced and freed
1971 	 * (which is achieved via the txg_wait_synced() call).
1972 	 */
1973 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1974 	txg_wait_synced(zilog->zl_dmu_pool, 0);
1975 	ASSERT3P(list_tail(&zilog->zl_lwb_list), ==, NULL);
1976 }
1977 
1978 /*
1979  * This function will traverse the commit list, creating new lwbs as
1980  * needed, and committing the itxs from the commit list to these newly
1981  * created lwbs. Additionally, as a new lwb is created, the previous
1982  * lwb will be issued to the zio layer to be written to disk.
1983  */
1984 static void
1985 zil_process_commit_list(zilog_t *zilog)
1986 {
1987 	spa_t *spa = zilog->zl_spa;
1988 	list_t nolwb_waiters;
1989 	lwb_t *lwb;
1990 	itx_t *itx;
1991 
1992 	ASSERT(MUTEX_HELD(&zilog->zl_issuer_lock));
1993 
1994 	/*
1995 	 * Return if there's nothing to commit before we dirty the fs by
1996 	 * calling zil_create().
1997 	 */
1998 	if (list_head(&zilog->zl_itx_commit_list) == NULL)
1999 		return;
2000 
2001 	list_create(&nolwb_waiters, sizeof (zil_commit_waiter_t),
2002 	    offsetof(zil_commit_waiter_t, zcw_node));
2003 
2004 	lwb = list_tail(&zilog->zl_lwb_list);
2005 	if (lwb == NULL) {
2006 		lwb = zil_create(zilog);
2007 	} else {
2008 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
2009 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_DONE);
2010 	}
2011 
2012 	while (itx = list_head(&zilog->zl_itx_commit_list)) {
2013 		lr_t *lrc = &itx->itx_lr;
2014 		uint64_t txg = lrc->lrc_txg;
2015 
2016 		ASSERT3U(txg, !=, 0);
2017 
2018 		if (lrc->lrc_txtype == TX_COMMIT) {
2019 			DTRACE_PROBE2(zil__process__commit__itx,
2020 			    zilog_t *, zilog, itx_t *, itx);
2021 		} else {
2022 			DTRACE_PROBE2(zil__process__normal__itx,
2023 			    zilog_t *, zilog, itx_t *, itx);
2024 		}
2025 
2026 		boolean_t synced = txg <= spa_last_synced_txg(spa);
2027 		boolean_t frozen = txg > spa_freeze_txg(spa);
2028 
2029 		/*
2030 		 * If the txg of this itx has already been synced out, then
2031 		 * we don't need to commit this itx to an lwb. This is
2032 		 * because the data of this itx will have already been
2033 		 * written to the main pool. This is inherently racy, and
2034 		 * it's still ok to commit an itx whose txg has already
2035 		 * been synced; this will result in a write that's
2036 		 * unnecessary, but will do no harm.
2037 		 *
2038 		 * With that said, we always want to commit TX_COMMIT itxs
2039 		 * to an lwb, regardless of whether or not that itx's txg
2040 		 * has been synced out. We do this to ensure any OPENED lwb
2041 		 * will always have at least one zil_commit_waiter_t linked
2042 		 * to the lwb.
2043 		 *
2044 		 * As a counter-example, if we skipped TX_COMMIT itx's
2045 		 * whose txg had already been synced, the following
2046 		 * situation could occur if we happened to be racing with
2047 		 * spa_sync:
2048 		 *
2049 		 * 1. we commit a non-TX_COMMIT itx to an lwb, where the
2050 		 *    itx's txg is 10 and the last synced txg is 9.
2051 		 * 2. spa_sync finishes syncing out txg 10.
2052 		 * 3. we move to the next itx in the list, it's a TX_COMMIT
2053 		 *    whose txg is 10, so we skip it rather than committing
2054 		 *    it to the lwb used in (1).
2055 		 *
2056 		 * If the itx that is skipped in (3) is the last TX_COMMIT
2057 		 * itx in the commit list, than it's possible for the lwb
2058 		 * used in (1) to remain in the OPENED state indefinitely.
2059 		 *
2060 		 * To prevent the above scenario from occuring, ensuring
2061 		 * that once an lwb is OPENED it will transition to ISSUED
2062 		 * and eventually DONE, we always commit TX_COMMIT itx's to
2063 		 * an lwb here, even if that itx's txg has already been
2064 		 * synced.
2065 		 *
2066 		 * Finally, if the pool is frozen, we _always_ commit the
2067 		 * itx.  The point of freezing the pool is to prevent data
2068 		 * from being written to the main pool via spa_sync, and
2069 		 * instead rely solely on the ZIL to persistently store the
2070 		 * data; i.e.  when the pool is frozen, the last synced txg
2071 		 * value can't be trusted.
2072 		 */
2073 		if (frozen || !synced || lrc->lrc_txtype == TX_COMMIT) {
2074 			if (lwb != NULL) {
2075 				lwb = zil_lwb_commit(zilog, itx, lwb);
2076 			} else if (lrc->lrc_txtype == TX_COMMIT) {
2077 				ASSERT3P(lwb, ==, NULL);
2078 				zil_commit_waiter_link_nolwb(
2079 				    itx->itx_private, &nolwb_waiters);
2080 			}
2081 		}
2082 
2083 		list_remove(&zilog->zl_itx_commit_list, itx);
2084 		zil_itx_destroy(itx);
2085 	}
2086 
2087 	if (lwb == NULL) {
2088 		/*
2089 		 * This indicates zio_alloc_zil() failed to allocate the
2090 		 * "next" lwb on-disk. When this happens, we must stall
2091 		 * the ZIL write pipeline; see the comment within
2092 		 * zil_commit_writer_stall() for more details.
2093 		 */
2094 		zil_commit_writer_stall(zilog);
2095 
2096 		/*
2097 		 * Additionally, we have to signal and mark the "nolwb"
2098 		 * waiters as "done" here, since without an lwb, we
2099 		 * can't do this via zil_lwb_flush_vdevs_done() like
2100 		 * normal.
2101 		 */
2102 		zil_commit_waiter_t *zcw;
2103 		while (zcw = list_head(&nolwb_waiters)) {
2104 			zil_commit_waiter_skip(zcw);
2105 			list_remove(&nolwb_waiters, zcw);
2106 		}
2107 	} else {
2108 		ASSERT(list_is_empty(&nolwb_waiters));
2109 		ASSERT3P(lwb, !=, NULL);
2110 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
2111 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_DONE);
2112 
2113 		/*
2114 		 * At this point, the ZIL block pointed at by the "lwb"
2115 		 * variable is in one of the following states: "closed"
2116 		 * or "open".
2117 		 *
2118 		 * If its "closed", then no itxs have been committed to
2119 		 * it, so there's no point in issuing its zio (i.e.
2120 		 * it's "empty").
2121 		 *
2122 		 * If its "open" state, then it contains one or more
2123 		 * itxs that eventually need to be committed to stable
2124 		 * storage. In this case we intentionally do not issue
2125 		 * the lwb's zio to disk yet, and instead rely on one of
2126 		 * the following two mechanisms for issuing the zio:
2127 		 *
2128 		 * 1. Ideally, there will be more ZIL activity occuring
2129 		 * on the system, such that this function will be
2130 		 * immediately called again (not necessarily by the same
2131 		 * thread) and this lwb's zio will be issued via
2132 		 * zil_lwb_commit(). This way, the lwb is guaranteed to
2133 		 * be "full" when it is issued to disk, and we'll make
2134 		 * use of the lwb's size the best we can.
2135 		 *
2136 		 * 2. If there isn't sufficient ZIL activity occuring on
2137 		 * the system, such that this lwb's zio isn't issued via
2138 		 * zil_lwb_commit(), zil_commit_waiter() will issue the
2139 		 * lwb's zio. If this occurs, the lwb is not guaranteed
2140 		 * to be "full" by the time its zio is issued, and means
2141 		 * the size of the lwb was "too large" given the amount
2142 		 * of ZIL activity occuring on the system at that time.
2143 		 *
2144 		 * We do this for a couple of reasons:
2145 		 *
2146 		 * 1. To try and reduce the number of IOPs needed to
2147 		 * write the same number of itxs. If an lwb has space
2148 		 * available in it's buffer for more itxs, and more itxs
2149 		 * will be committed relatively soon (relative to the
2150 		 * latency of performing a write), then it's beneficial
2151 		 * to wait for these "next" itxs. This way, more itxs
2152 		 * can be committed to stable storage with fewer writes.
2153 		 *
2154 		 * 2. To try and use the largest lwb block size that the
2155 		 * incoming rate of itxs can support. Again, this is to
2156 		 * try and pack as many itxs into as few lwbs as
2157 		 * possible, without significantly impacting the latency
2158 		 * of each individual itx.
2159 		 */
2160 	}
2161 }
2162 
2163 /*
2164  * This function is responsible for ensuring the passed in commit waiter
2165  * (and associated commit itx) is committed to an lwb. If the waiter is
2166  * not already committed to an lwb, all itxs in the zilog's queue of
2167  * itxs will be processed. The assumption is the passed in waiter's
2168  * commit itx will found in the queue just like the other non-commit
2169  * itxs, such that when the entire queue is processed, the waiter will
2170  * have been commited to an lwb.
2171  *
2172  * The lwb associated with the passed in waiter is not guaranteed to
2173  * have been issued by the time this function completes. If the lwb is
2174  * not issued, we rely on future calls to zil_commit_writer() to issue
2175  * the lwb, or the timeout mechanism found in zil_commit_waiter().
2176  */
2177 static void
2178 zil_commit_writer(zilog_t *zilog, zil_commit_waiter_t *zcw)
2179 {
2180 	ASSERT(!MUTEX_HELD(&zilog->zl_lock));
2181 	ASSERT(spa_writeable(zilog->zl_spa));
2182 
2183 	mutex_enter(&zilog->zl_issuer_lock);
2184 
2185 	if (zcw->zcw_lwb != NULL || zcw->zcw_done) {
2186 		/*
2187 		 * It's possible that, while we were waiting to acquire
2188 		 * the "zl_issuer_lock", another thread committed this
2189 		 * waiter to an lwb. If that occurs, we bail out early,
2190 		 * without processing any of the zilog's queue of itxs.
2191 		 *
2192 		 * On certain workloads and system configurations, the
2193 		 * "zl_issuer_lock" can become highly contended. In an
2194 		 * attempt to reduce this contention, we immediately drop
2195 		 * the lock if the waiter has already been processed.
2196 		 *
2197 		 * We've measured this optimization to reduce CPU spent
2198 		 * contending on this lock by up to 5%, using a system
2199 		 * with 32 CPUs, low latency storage (~50 usec writes),
2200 		 * and 1024 threads performing sync writes.
2201 		 */
2202 		goto out;
2203 	}
2204 
2205 	zil_get_commit_list(zilog);
2206 	zil_prune_commit_list(zilog);
2207 	zil_process_commit_list(zilog);
2208 
2209 out:
2210 	mutex_exit(&zilog->zl_issuer_lock);
2211 }
2212 
2213 static void
2214 zil_commit_waiter_timeout(zilog_t *zilog, zil_commit_waiter_t *zcw)
2215 {
2216 	ASSERT(!MUTEX_HELD(&zilog->zl_issuer_lock));
2217 	ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2218 	ASSERT3B(zcw->zcw_done, ==, B_FALSE);
2219 
2220 	lwb_t *lwb = zcw->zcw_lwb;
2221 	ASSERT3P(lwb, !=, NULL);
2222 	ASSERT3S(lwb->lwb_state, !=, LWB_STATE_CLOSED);
2223 
2224 	/*
2225 	 * If the lwb has already been issued by another thread, we can
2226 	 * immediately return since there's no work to be done (the
2227 	 * point of this function is to issue the lwb). Additionally, we
2228 	 * do this prior to acquiring the zl_issuer_lock, to avoid
2229 	 * acquiring it when it's not necessary to do so.
2230 	 */
2231 	if (lwb->lwb_state == LWB_STATE_ISSUED ||
2232 	    lwb->lwb_state == LWB_STATE_DONE)
2233 		return;
2234 
2235 	/*
2236 	 * In order to call zil_lwb_write_issue() we must hold the
2237 	 * zilog's "zl_issuer_lock". We can't simply acquire that lock,
2238 	 * since we're already holding the commit waiter's "zcw_lock",
2239 	 * and those two locks are aquired in the opposite order
2240 	 * elsewhere.
2241 	 */
2242 	mutex_exit(&zcw->zcw_lock);
2243 	mutex_enter(&zilog->zl_issuer_lock);
2244 	mutex_enter(&zcw->zcw_lock);
2245 
2246 	/*
2247 	 * Since we just dropped and re-acquired the commit waiter's
2248 	 * lock, we have to re-check to see if the waiter was marked
2249 	 * "done" during that process. If the waiter was marked "done",
2250 	 * the "lwb" pointer is no longer valid (it can be free'd after
2251 	 * the waiter is marked "done"), so without this check we could
2252 	 * wind up with a use-after-free error below.
2253 	 */
2254 	if (zcw->zcw_done)
2255 		goto out;
2256 
2257 	ASSERT3P(lwb, ==, zcw->zcw_lwb);
2258 
2259 	/*
2260 	 * We've already checked this above, but since we hadn't acquired
2261 	 * the zilog's zl_issuer_lock, we have to perform this check a
2262 	 * second time while holding the lock.
2263 	 *
2264 	 * We don't need to hold the zl_lock since the lwb cannot transition
2265 	 * from OPENED to ISSUED while we hold the zl_issuer_lock. The lwb
2266 	 * _can_ transition from ISSUED to DONE, but it's OK to race with
2267 	 * that transition since we treat the lwb the same, whether it's in
2268 	 * the ISSUED or DONE states.
2269 	 *
2270 	 * The important thing, is we treat the lwb differently depending on
2271 	 * if it's ISSUED or OPENED, and block any other threads that might
2272 	 * attempt to issue this lwb. For that reason we hold the
2273 	 * zl_issuer_lock when checking the lwb_state; we must not call
2274 	 * zil_lwb_write_issue() if the lwb had already been issued.
2275 	 *
2276 	 * See the comment above the lwb_state_t structure definition for
2277 	 * more details on the lwb states, and locking requirements.
2278 	 */
2279 	if (lwb->lwb_state == LWB_STATE_ISSUED ||
2280 	    lwb->lwb_state == LWB_STATE_DONE)
2281 		goto out;
2282 
2283 	ASSERT3S(lwb->lwb_state, ==, LWB_STATE_OPENED);
2284 
2285 	/*
2286 	 * As described in the comments above zil_commit_waiter() and
2287 	 * zil_process_commit_list(), we need to issue this lwb's zio
2288 	 * since we've reached the commit waiter's timeout and it still
2289 	 * hasn't been issued.
2290 	 */
2291 	lwb_t *nlwb = zil_lwb_write_issue(zilog, lwb);
2292 
2293 	IMPLY(nlwb != NULL, lwb->lwb_state != LWB_STATE_OPENED);
2294 
2295 	/*
2296 	 * Since the lwb's zio hadn't been issued by the time this thread
2297 	 * reached its timeout, we reset the zilog's "zl_cur_used" field
2298 	 * to influence the zil block size selection algorithm.
2299 	 *
2300 	 * By having to issue the lwb's zio here, it means the size of the
2301 	 * lwb was too large, given the incoming throughput of itxs.  By
2302 	 * setting "zl_cur_used" to zero, we communicate this fact to the
2303 	 * block size selection algorithm, so it can take this informaiton
2304 	 * into account, and potentially select a smaller size for the
2305 	 * next lwb block that is allocated.
2306 	 */
2307 	zilog->zl_cur_used = 0;
2308 
2309 	if (nlwb == NULL) {
2310 		/*
2311 		 * When zil_lwb_write_issue() returns NULL, this
2312 		 * indicates zio_alloc_zil() failed to allocate the
2313 		 * "next" lwb on-disk. When this occurs, the ZIL write
2314 		 * pipeline must be stalled; see the comment within the
2315 		 * zil_commit_writer_stall() function for more details.
2316 		 *
2317 		 * We must drop the commit waiter's lock prior to
2318 		 * calling zil_commit_writer_stall() or else we can wind
2319 		 * up with the following deadlock:
2320 		 *
2321 		 * - This thread is waiting for the txg to sync while
2322 		 *   holding the waiter's lock; txg_wait_synced() is
2323 		 *   used within txg_commit_writer_stall().
2324 		 *
2325 		 * - The txg can't sync because it is waiting for this
2326 		 *   lwb's zio callback to call dmu_tx_commit().
2327 		 *
2328 		 * - The lwb's zio callback can't call dmu_tx_commit()
2329 		 *   because it's blocked trying to acquire the waiter's
2330 		 *   lock, which occurs prior to calling dmu_tx_commit()
2331 		 */
2332 		mutex_exit(&zcw->zcw_lock);
2333 		zil_commit_writer_stall(zilog);
2334 		mutex_enter(&zcw->zcw_lock);
2335 	}
2336 
2337 out:
2338 	mutex_exit(&zilog->zl_issuer_lock);
2339 	ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2340 }
2341 
2342 /*
2343  * This function is responsible for performing the following two tasks:
2344  *
2345  * 1. its primary responsibility is to block until the given "commit
2346  *    waiter" is considered "done".
2347  *
2348  * 2. its secondary responsibility is to issue the zio for the lwb that
2349  *    the given "commit waiter" is waiting on, if this function has
2350  *    waited "long enough" and the lwb is still in the "open" state.
2351  *
2352  * Given a sufficient amount of itxs being generated and written using
2353  * the ZIL, the lwb's zio will be issued via the zil_lwb_commit()
2354  * function. If this does not occur, this secondary responsibility will
2355  * ensure the lwb is issued even if there is not other synchronous
2356  * activity on the system.
2357  *
2358  * For more details, see zil_process_commit_list(); more specifically,
2359  * the comment at the bottom of that function.
2360  */
2361 static void
2362 zil_commit_waiter(zilog_t *zilog, zil_commit_waiter_t *zcw)
2363 {
2364 	ASSERT(!MUTEX_HELD(&zilog->zl_lock));
2365 	ASSERT(!MUTEX_HELD(&zilog->zl_issuer_lock));
2366 	ASSERT(spa_writeable(zilog->zl_spa));
2367 
2368 	mutex_enter(&zcw->zcw_lock);
2369 
2370 	/*
2371 	 * The timeout is scaled based on the lwb latency to avoid
2372 	 * significantly impacting the latency of each individual itx.
2373 	 * For more details, see the comment at the bottom of the
2374 	 * zil_process_commit_list() function.
2375 	 */
2376 	int pct = MAX(zfs_commit_timeout_pct, 1);
2377 	hrtime_t sleep = (zilog->zl_last_lwb_latency * pct) / 100;
2378 	hrtime_t wakeup = gethrtime() + sleep;
2379 	boolean_t timedout = B_FALSE;
2380 
2381 	while (!zcw->zcw_done) {
2382 		ASSERT(MUTEX_HELD(&zcw->zcw_lock));
2383 
2384 		lwb_t *lwb = zcw->zcw_lwb;
2385 
2386 		/*
2387 		 * Usually, the waiter will have a non-NULL lwb field here,
2388 		 * but it's possible for it to be NULL as a result of
2389 		 * zil_commit() racing with spa_sync().
2390 		 *
2391 		 * When zil_clean() is called, it's possible for the itxg
2392 		 * list (which may be cleaned via a taskq) to contain
2393 		 * commit itxs. When this occurs, the commit waiters linked
2394 		 * off of these commit itxs will not be committed to an
2395 		 * lwb.  Additionally, these commit waiters will not be
2396 		 * marked done until zil_commit_waiter_skip() is called via
2397 		 * zil_itxg_clean().
2398 		 *
2399 		 * Thus, it's possible for this commit waiter (i.e. the
2400 		 * "zcw" variable) to be found in this "in between" state;
2401 		 * where it's "zcw_lwb" field is NULL, and it hasn't yet
2402 		 * been skipped, so it's "zcw_done" field is still B_FALSE.
2403 		 */
2404 		IMPLY(lwb != NULL, lwb->lwb_state != LWB_STATE_CLOSED);
2405 
2406 		if (lwb != NULL && lwb->lwb_state == LWB_STATE_OPENED) {
2407 			ASSERT3B(timedout, ==, B_FALSE);
2408 
2409 			/*
2410 			 * If the lwb hasn't been issued yet, then we
2411 			 * need to wait with a timeout, in case this
2412 			 * function needs to issue the lwb after the
2413 			 * timeout is reached; responsibility (2) from
2414 			 * the comment above this function.
2415 			 */
2416 			clock_t timeleft = cv_timedwait_hires(&zcw->zcw_cv,
2417 			    &zcw->zcw_lock, wakeup, USEC2NSEC(1),
2418 			    CALLOUT_FLAG_ABSOLUTE);
2419 
2420 			if (timeleft >= 0 || zcw->zcw_done)
2421 				continue;
2422 
2423 			timedout = B_TRUE;
2424 			zil_commit_waiter_timeout(zilog, zcw);
2425 
2426 			if (!zcw->zcw_done) {
2427 				/*
2428 				 * If the commit waiter has already been
2429 				 * marked "done", it's possible for the
2430 				 * waiter's lwb structure to have already
2431 				 * been freed.  Thus, we can only reliably
2432 				 * make these assertions if the waiter
2433 				 * isn't done.
2434 				 */
2435 				ASSERT3P(lwb, ==, zcw->zcw_lwb);
2436 				ASSERT3S(lwb->lwb_state, !=, LWB_STATE_OPENED);
2437 			}
2438 		} else {
2439 			/*
2440 			 * If the lwb isn't open, then it must have already
2441 			 * been issued. In that case, there's no need to
2442 			 * use a timeout when waiting for the lwb to
2443 			 * complete.
2444 			 *
2445 			 * Additionally, if the lwb is NULL, the waiter
2446 			 * will soon be signalled and marked done via
2447 			 * zil_clean() and zil_itxg_clean(), so no timeout
2448 			 * is required.
2449 			 */
2450 
2451 			IMPLY(lwb != NULL,
2452 			    lwb->lwb_state == LWB_STATE_ISSUED ||
2453 			    lwb->lwb_state == LWB_STATE_DONE);
2454 			cv_wait(&zcw->zcw_cv, &zcw->zcw_lock);
2455 		}
2456 	}
2457 
2458 	mutex_exit(&zcw->zcw_lock);
2459 }
2460 
2461 static zil_commit_waiter_t *
2462 zil_alloc_commit_waiter()
2463 {
2464 	zil_commit_waiter_t *zcw = kmem_cache_alloc(zil_zcw_cache, KM_SLEEP);
2465 
2466 	cv_init(&zcw->zcw_cv, NULL, CV_DEFAULT, NULL);
2467 	mutex_init(&zcw->zcw_lock, NULL, MUTEX_DEFAULT, NULL);
2468 	list_link_init(&zcw->zcw_node);
2469 	zcw->zcw_lwb = NULL;
2470 	zcw->zcw_done = B_FALSE;
2471 	zcw->zcw_zio_error = 0;
2472 
2473 	return (zcw);
2474 }
2475 
2476 static void
2477 zil_free_commit_waiter(zil_commit_waiter_t *zcw)
2478 {
2479 	ASSERT(!list_link_active(&zcw->zcw_node));
2480 	ASSERT3P(zcw->zcw_lwb, ==, NULL);
2481 	ASSERT3B(zcw->zcw_done, ==, B_TRUE);
2482 	mutex_destroy(&zcw->zcw_lock);
2483 	cv_destroy(&zcw->zcw_cv);
2484 	kmem_cache_free(zil_zcw_cache, zcw);
2485 }
2486 
2487 /*
2488  * This function is used to create a TX_COMMIT itx and assign it. This
2489  * way, it will be linked into the ZIL's list of synchronous itxs, and
2490  * then later committed to an lwb (or skipped) when
2491  * zil_process_commit_list() is called.
2492  */
2493 static void
2494 zil_commit_itx_assign(zilog_t *zilog, zil_commit_waiter_t *zcw)
2495 {
2496 	dmu_tx_t *tx = dmu_tx_create(zilog->zl_os);
2497 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
2498 
2499 	itx_t *itx = zil_itx_create(TX_COMMIT, sizeof (lr_t));
2500 	itx->itx_sync = B_TRUE;
2501 	itx->itx_private = zcw;
2502 
2503 	zil_itx_assign(zilog, itx, tx);
2504 
2505 	dmu_tx_commit(tx);
2506 }
2507 
2508 /*
2509  * Commit ZFS Intent Log transactions (itxs) to stable storage.
2510  *
2511  * When writing ZIL transactions to the on-disk representation of the
2512  * ZIL, the itxs are committed to a Log Write Block (lwb). Multiple
2513  * itxs can be committed to a single lwb. Once a lwb is written and
2514  * committed to stable storage (i.e. the lwb is written, and vdevs have
2515  * been flushed), each itx that was committed to that lwb is also
2516  * considered to be committed to stable storage.
2517  *
2518  * When an itx is committed to an lwb, the log record (lr_t) contained
2519  * by the itx is copied into the lwb's zio buffer, and once this buffer
2520  * is written to disk, it becomes an on-disk ZIL block.
2521  *
2522  * As itxs are generated, they're inserted into the ZIL's queue of
2523  * uncommitted itxs. The semantics of zil_commit() are such that it will
2524  * block until all itxs that were in the queue when it was called, are
2525  * committed to stable storage.
2526  *
2527  * If "foid" is zero, this means all "synchronous" and "asynchronous"
2528  * itxs, for all objects in the dataset, will be committed to stable
2529  * storage prior to zil_commit() returning. If "foid" is non-zero, all
2530  * "synchronous" itxs for all objects, but only "asynchronous" itxs
2531  * that correspond to the foid passed in, will be committed to stable
2532  * storage prior to zil_commit() returning.
2533  *
2534  * Generally speaking, when zil_commit() is called, the consumer doesn't
2535  * actually care about _all_ of the uncommitted itxs. Instead, they're
2536  * simply trying to waiting for a specific itx to be committed to disk,
2537  * but the interface(s) for interacting with the ZIL don't allow such
2538  * fine-grained communication. A better interface would allow a consumer
2539  * to create and assign an itx, and then pass a reference to this itx to
2540  * zil_commit(); such that zil_commit() would return as soon as that
2541  * specific itx was committed to disk (instead of waiting for _all_
2542  * itxs to be committed).
2543  *
2544  * When a thread calls zil_commit() a special "commit itx" will be
2545  * generated, along with a corresponding "waiter" for this commit itx.
2546  * zil_commit() will wait on this waiter's CV, such that when the waiter
2547  * is marked done, and signalled, zil_commit() will return.
2548  *
2549  * This commit itx is inserted into the queue of uncommitted itxs. This
2550  * provides an easy mechanism for determining which itxs were in the
2551  * queue prior to zil_commit() having been called, and which itxs were
2552  * added after zil_commit() was called.
2553  *
2554  * The commit it is special; it doesn't have any on-disk representation.
2555  * When a commit itx is "committed" to an lwb, the waiter associated
2556  * with it is linked onto the lwb's list of waiters. Then, when that lwb
2557  * completes, each waiter on the lwb's list is marked done and signalled
2558  * -- allowing the thread waiting on the waiter to return from zil_commit().
2559  *
2560  * It's important to point out a few critical factors that allow us
2561  * to make use of the commit itxs, commit waiters, per-lwb lists of
2562  * commit waiters, and zio completion callbacks like we're doing:
2563  *
2564  *   1. The list of waiters for each lwb is traversed, and each commit
2565  *      waiter is marked "done" and signalled, in the zio completion
2566  *      callback of the lwb's zio[*].
2567  *
2568  *      * Actually, the waiters are signalled in the zio completion
2569  *        callback of the root zio for the DKIOCFLUSHWRITECACHE commands
2570  *        that are sent to the vdevs upon completion of the lwb zio.
2571  *
2572  *   2. When the itxs are inserted into the ZIL's queue of uncommitted
2573  *      itxs, the order in which they are inserted is preserved[*]; as
2574  *      itxs are added to the queue, they are added to the tail of
2575  *      in-memory linked lists.
2576  *
2577  *      When committing the itxs to lwbs (to be written to disk), they
2578  *      are committed in the same order in which the itxs were added to
2579  *      the uncommitted queue's linked list(s); i.e. the linked list of
2580  *      itxs to commit is traversed from head to tail, and each itx is
2581  *      committed to an lwb in that order.
2582  *
2583  *      * To clarify:
2584  *
2585  *        - the order of "sync" itxs is preserved w.r.t. other
2586  *          "sync" itxs, regardless of the corresponding objects.
2587  *        - the order of "async" itxs is preserved w.r.t. other
2588  *          "async" itxs corresponding to the same object.
2589  *        - the order of "async" itxs is *not* preserved w.r.t. other
2590  *          "async" itxs corresponding to different objects.
2591  *        - the order of "sync" itxs w.r.t. "async" itxs (or vice
2592  *          versa) is *not* preserved, even for itxs that correspond
2593  *          to the same object.
2594  *
2595  *      For more details, see: zil_itx_assign(), zil_async_to_sync(),
2596  *      zil_get_commit_list(), and zil_process_commit_list().
2597  *
2598  *   3. The lwbs represent a linked list of blocks on disk. Thus, any
2599  *      lwb cannot be considered committed to stable storage, until its
2600  *      "previous" lwb is also committed to stable storage. This fact,
2601  *      coupled with the fact described above, means that itxs are
2602  *      committed in (roughly) the order in which they were generated.
2603  *      This is essential because itxs are dependent on prior itxs.
2604  *      Thus, we *must not* deem an itx as being committed to stable
2605  *      storage, until *all* prior itxs have also been committed to
2606  *      stable storage.
2607  *
2608  *      To enforce this ordering of lwb zio's, while still leveraging as
2609  *      much of the underlying storage performance as possible, we rely
2610  *      on two fundamental concepts:
2611  *
2612  *          1. The creation and issuance of lwb zio's is protected by
2613  *             the zilog's "zl_issuer_lock", which ensures only a single
2614  *             thread is creating and/or issuing lwb's at a time
2615  *          2. The "previous" lwb is a child of the "current" lwb
2616  *             (leveraging the zio parent-child depenency graph)
2617  *
2618  *      By relying on this parent-child zio relationship, we can have
2619  *      many lwb zio's concurrently issued to the underlying storage,
2620  *      but the order in which they complete will be the same order in
2621  *      which they were created.
2622  */
2623 void
2624 zil_commit(zilog_t *zilog, uint64_t foid)
2625 {
2626 	/*
2627 	 * We should never attempt to call zil_commit on a snapshot for
2628 	 * a couple of reasons:
2629 	 *
2630 	 * 1. A snapshot may never be modified, thus it cannot have any
2631 	 *    in-flight itxs that would have modified the dataset.
2632 	 *
2633 	 * 2. By design, when zil_commit() is called, a commit itx will
2634 	 *    be assigned to this zilog; as a result, the zilog will be
2635 	 *    dirtied. We must not dirty the zilog of a snapshot; there's
2636 	 *    checks in the code that enforce this invariant, and will
2637 	 *    cause a panic if it's not upheld.
2638 	 */
2639 	ASSERT3B(dmu_objset_is_snapshot(zilog->zl_os), ==, B_FALSE);
2640 
2641 	if (zilog->zl_sync == ZFS_SYNC_DISABLED)
2642 		return;
2643 
2644 	if (!spa_writeable(zilog->zl_spa)) {
2645 		/*
2646 		 * If the SPA is not writable, there should never be any
2647 		 * pending itxs waiting to be committed to disk. If that
2648 		 * weren't true, we'd skip writing those itxs out, and
2649 		 * would break the sematics of zil_commit(); thus, we're
2650 		 * verifying that truth before we return to the caller.
2651 		 */
2652 		ASSERT(list_is_empty(&zilog->zl_lwb_list));
2653 		ASSERT3P(zilog->zl_last_lwb_opened, ==, NULL);
2654 		for (int i = 0; i < TXG_SIZE; i++)
2655 			ASSERT3P(zilog->zl_itxg[i].itxg_itxs, ==, NULL);
2656 		return;
2657 	}
2658 
2659 	/*
2660 	 * If the ZIL is suspended, we don't want to dirty it by calling
2661 	 * zil_commit_itx_assign() below, nor can we write out
2662 	 * lwbs like would be done in zil_commit_write(). Thus, we
2663 	 * simply rely on txg_wait_synced() to maintain the necessary
2664 	 * semantics, and avoid calling those functions altogether.
2665 	 */
2666 	if (zilog->zl_suspend > 0) {
2667 		txg_wait_synced(zilog->zl_dmu_pool, 0);
2668 		return;
2669 	}
2670 
2671 	zil_commit_impl(zilog, foid);
2672 }
2673 
2674 void
2675 zil_commit_impl(zilog_t *zilog, uint64_t foid)
2676 {
2677 	/*
2678 	 * Move the "async" itxs for the specified foid to the "sync"
2679 	 * queues, such that they will be later committed (or skipped)
2680 	 * to an lwb when zil_process_commit_list() is called.
2681 	 *
2682 	 * Since these "async" itxs must be committed prior to this
2683 	 * call to zil_commit returning, we must perform this operation
2684 	 * before we call zil_commit_itx_assign().
2685 	 */
2686 	zil_async_to_sync(zilog, foid);
2687 
2688 	/*
2689 	 * We allocate a new "waiter" structure which will initially be
2690 	 * linked to the commit itx using the itx's "itx_private" field.
2691 	 * Since the commit itx doesn't represent any on-disk state,
2692 	 * when it's committed to an lwb, rather than copying the its
2693 	 * lr_t into the lwb's buffer, the commit itx's "waiter" will be
2694 	 * added to the lwb's list of waiters. Then, when the lwb is
2695 	 * committed to stable storage, each waiter in the lwb's list of
2696 	 * waiters will be marked "done", and signalled.
2697 	 *
2698 	 * We must create the waiter and assign the commit itx prior to
2699 	 * calling zil_commit_writer(), or else our specific commit itx
2700 	 * is not guaranteed to be committed to an lwb prior to calling
2701 	 * zil_commit_waiter().
2702 	 */
2703 	zil_commit_waiter_t *zcw = zil_alloc_commit_waiter();
2704 	zil_commit_itx_assign(zilog, zcw);
2705 
2706 	zil_commit_writer(zilog, zcw);
2707 	zil_commit_waiter(zilog, zcw);
2708 
2709 	if (zcw->zcw_zio_error != 0) {
2710 		/*
2711 		 * If there was an error writing out the ZIL blocks that
2712 		 * this thread is waiting on, then we fallback to
2713 		 * relying on spa_sync() to write out the data this
2714 		 * thread is waiting on. Obviously this has performance
2715 		 * implications, but the expectation is for this to be
2716 		 * an exceptional case, and shouldn't occur often.
2717 		 */
2718 		DTRACE_PROBE2(zil__commit__io__error,
2719 		    zilog_t *, zilog, zil_commit_waiter_t *, zcw);
2720 		txg_wait_synced(zilog->zl_dmu_pool, 0);
2721 	}
2722 
2723 	zil_free_commit_waiter(zcw);
2724 }
2725 
2726 /*
2727  * Called in syncing context to free committed log blocks and update log header.
2728  */
2729 void
2730 zil_sync(zilog_t *zilog, dmu_tx_t *tx)
2731 {
2732 	zil_header_t *zh = zil_header_in_syncing_context(zilog);
2733 	uint64_t txg = dmu_tx_get_txg(tx);
2734 	spa_t *spa = zilog->zl_spa;
2735 	uint64_t *replayed_seq = &zilog->zl_replayed_seq[txg & TXG_MASK];
2736 	lwb_t *lwb;
2737 
2738 	/*
2739 	 * We don't zero out zl_destroy_txg, so make sure we don't try
2740 	 * to destroy it twice.
2741 	 */
2742 	if (spa_sync_pass(spa) != 1)
2743 		return;
2744 
2745 	mutex_enter(&zilog->zl_lock);
2746 
2747 	ASSERT(zilog->zl_stop_sync == 0);
2748 
2749 	if (*replayed_seq != 0) {
2750 		ASSERT(zh->zh_replay_seq < *replayed_seq);
2751 		zh->zh_replay_seq = *replayed_seq;
2752 		*replayed_seq = 0;
2753 	}
2754 
2755 	if (zilog->zl_destroy_txg == txg) {
2756 		blkptr_t blk = zh->zh_log;
2757 
2758 		ASSERT(list_head(&zilog->zl_lwb_list) == NULL);
2759 
2760 		bzero(zh, sizeof (zil_header_t));
2761 		bzero(zilog->zl_replayed_seq, sizeof (zilog->zl_replayed_seq));
2762 
2763 		if (zilog->zl_keep_first) {
2764 			/*
2765 			 * If this block was part of log chain that couldn't
2766 			 * be claimed because a device was missing during
2767 			 * zil_claim(), but that device later returns,
2768 			 * then this block could erroneously appear valid.
2769 			 * To guard against this, assign a new GUID to the new
2770 			 * log chain so it doesn't matter what blk points to.
2771 			 */
2772 			zil_init_log_chain(zilog, &blk);
2773 			zh->zh_log = blk;
2774 		}
2775 	}
2776 
2777 	while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
2778 		zh->zh_log = lwb->lwb_blk;
2779 		if (lwb->lwb_buf != NULL || lwb->lwb_max_txg > txg)
2780 			break;
2781 		list_remove(&zilog->zl_lwb_list, lwb);
2782 		zio_free(spa, txg, &lwb->lwb_blk);
2783 		zil_free_lwb(zilog, lwb);
2784 
2785 		/*
2786 		 * If we don't have anything left in the lwb list then
2787 		 * we've had an allocation failure and we need to zero
2788 		 * out the zil_header blkptr so that we don't end
2789 		 * up freeing the same block twice.
2790 		 */
2791 		if (list_head(&zilog->zl_lwb_list) == NULL)
2792 			BP_ZERO(&zh->zh_log);
2793 	}
2794 	mutex_exit(&zilog->zl_lock);
2795 }
2796 
2797 /* ARGSUSED */
2798 static int
2799 zil_lwb_cons(void *vbuf, void *unused, int kmflag)
2800 {
2801 	lwb_t *lwb = vbuf;
2802 	list_create(&lwb->lwb_waiters, sizeof (zil_commit_waiter_t),
2803 	    offsetof(zil_commit_waiter_t, zcw_node));
2804 	avl_create(&lwb->lwb_vdev_tree, zil_lwb_vdev_compare,
2805 	    sizeof (zil_vdev_node_t), offsetof(zil_vdev_node_t, zv_node));
2806 	mutex_init(&lwb->lwb_vdev_lock, NULL, MUTEX_DEFAULT, NULL);
2807 	return (0);
2808 }
2809 
2810 /* ARGSUSED */
2811 static void
2812 zil_lwb_dest(void *vbuf, void *unused)
2813 {
2814 	lwb_t *lwb = vbuf;
2815 	mutex_destroy(&lwb->lwb_vdev_lock);
2816 	avl_destroy(&lwb->lwb_vdev_tree);
2817 	list_destroy(&lwb->lwb_waiters);
2818 }
2819 
2820 void
2821 zil_init(void)
2822 {
2823 	zil_lwb_cache = kmem_cache_create("zil_lwb_cache",
2824 	    sizeof (lwb_t), 0, zil_lwb_cons, zil_lwb_dest, NULL, NULL, NULL, 0);
2825 
2826 	zil_zcw_cache = kmem_cache_create("zil_zcw_cache",
2827 	    sizeof (zil_commit_waiter_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
2828 }
2829 
2830 void
2831 zil_fini(void)
2832 {
2833 	kmem_cache_destroy(zil_zcw_cache);
2834 	kmem_cache_destroy(zil_lwb_cache);
2835 }
2836 
2837 void
2838 zil_set_sync(zilog_t *zilog, uint64_t sync)
2839 {
2840 	zilog->zl_sync = sync;
2841 }
2842 
2843 void
2844 zil_set_logbias(zilog_t *zilog, uint64_t logbias)
2845 {
2846 	zilog->zl_logbias = logbias;
2847 }
2848 
2849 zilog_t *
2850 zil_alloc(objset_t *os, zil_header_t *zh_phys)
2851 {
2852 	zilog_t *zilog;
2853 
2854 	zilog = kmem_zalloc(sizeof (zilog_t), KM_SLEEP);
2855 
2856 	zilog->zl_header = zh_phys;
2857 	zilog->zl_os = os;
2858 	zilog->zl_spa = dmu_objset_spa(os);
2859 	zilog->zl_dmu_pool = dmu_objset_pool(os);
2860 	zilog->zl_destroy_txg = TXG_INITIAL - 1;
2861 	zilog->zl_logbias = dmu_objset_logbias(os);
2862 	zilog->zl_sync = dmu_objset_syncprop(os);
2863 	zilog->zl_dirty_max_txg = 0;
2864 	zilog->zl_last_lwb_opened = NULL;
2865 	zilog->zl_last_lwb_latency = 0;
2866 
2867 	mutex_init(&zilog->zl_lock, NULL, MUTEX_DEFAULT, NULL);
2868 	mutex_init(&zilog->zl_issuer_lock, NULL, MUTEX_DEFAULT, NULL);
2869 
2870 	for (int i = 0; i < TXG_SIZE; i++) {
2871 		mutex_init(&zilog->zl_itxg[i].itxg_lock, NULL,
2872 		    MUTEX_DEFAULT, NULL);
2873 	}
2874 
2875 	list_create(&zilog->zl_lwb_list, sizeof (lwb_t),
2876 	    offsetof(lwb_t, lwb_node));
2877 
2878 	list_create(&zilog->zl_itx_commit_list, sizeof (itx_t),
2879 	    offsetof(itx_t, itx_node));
2880 
2881 	cv_init(&zilog->zl_cv_suspend, NULL, CV_DEFAULT, NULL);
2882 
2883 	return (zilog);
2884 }
2885 
2886 void
2887 zil_free(zilog_t *zilog)
2888 {
2889 	zilog->zl_stop_sync = 1;
2890 
2891 	ASSERT0(zilog->zl_suspend);
2892 	ASSERT0(zilog->zl_suspending);
2893 
2894 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
2895 	list_destroy(&zilog->zl_lwb_list);
2896 
2897 	ASSERT(list_is_empty(&zilog->zl_itx_commit_list));
2898 	list_destroy(&zilog->zl_itx_commit_list);
2899 
2900 	for (int i = 0; i < TXG_SIZE; i++) {
2901 		/*
2902 		 * It's possible for an itx to be generated that doesn't dirty
2903 		 * a txg (e.g. ztest TX_TRUNCATE). So there's no zil_clean()
2904 		 * callback to remove the entry. We remove those here.
2905 		 *
2906 		 * Also free up the ziltest itxs.
2907 		 */
2908 		if (zilog->zl_itxg[i].itxg_itxs)
2909 			zil_itxg_clean(zilog->zl_itxg[i].itxg_itxs);
2910 		mutex_destroy(&zilog->zl_itxg[i].itxg_lock);
2911 	}
2912 
2913 	mutex_destroy(&zilog->zl_issuer_lock);
2914 	mutex_destroy(&zilog->zl_lock);
2915 
2916 	cv_destroy(&zilog->zl_cv_suspend);
2917 
2918 	kmem_free(zilog, sizeof (zilog_t));
2919 }
2920 
2921 /*
2922  * Open an intent log.
2923  */
2924 zilog_t *
2925 zil_open(objset_t *os, zil_get_data_t *get_data)
2926 {
2927 	zilog_t *zilog = dmu_objset_zil(os);
2928 
2929 	ASSERT3P(zilog->zl_get_data, ==, NULL);
2930 	ASSERT3P(zilog->zl_last_lwb_opened, ==, NULL);
2931 	ASSERT(list_is_empty(&zilog->zl_lwb_list));
2932 
2933 	zilog->zl_get_data = get_data;
2934 
2935 	return (zilog);
2936 }
2937 
2938 /*
2939  * Close an intent log.
2940  */
2941 void
2942 zil_close(zilog_t *zilog)
2943 {
2944 	lwb_t *lwb;
2945 	uint64_t txg;
2946 
2947 	if (!dmu_objset_is_snapshot(zilog->zl_os)) {
2948 		zil_commit(zilog, 0);
2949 	} else {
2950 		ASSERT3P(list_tail(&zilog->zl_lwb_list), ==, NULL);
2951 		ASSERT0(zilog->zl_dirty_max_txg);
2952 		ASSERT3B(zilog_is_dirty(zilog), ==, B_FALSE);
2953 	}
2954 
2955 	mutex_enter(&zilog->zl_lock);
2956 	lwb = list_tail(&zilog->zl_lwb_list);
2957 	if (lwb == NULL)
2958 		txg = zilog->zl_dirty_max_txg;
2959 	else
2960 		txg = MAX(zilog->zl_dirty_max_txg, lwb->lwb_max_txg);
2961 	mutex_exit(&zilog->zl_lock);
2962 
2963 	/*
2964 	 * We need to use txg_wait_synced() to wait long enough for the
2965 	 * ZIL to be clean, and to wait for all pending lwbs to be
2966 	 * written out.
2967 	 */
2968 	if (txg != 0)
2969 		txg_wait_synced(zilog->zl_dmu_pool, txg);
2970 
2971 	if (zilog_is_dirty(zilog))
2972 		zfs_dbgmsg("zil (%p) is dirty, txg %llu", zilog, txg);
2973 	VERIFY(!zilog_is_dirty(zilog));
2974 
2975 	zilog->zl_get_data = NULL;
2976 
2977 	/*
2978 	 * We should have only one lwb left on the list; remove it now.
2979 	 */
2980 	mutex_enter(&zilog->zl_lock);
2981 	lwb = list_head(&zilog->zl_lwb_list);
2982 	if (lwb != NULL) {
2983 		ASSERT3P(lwb, ==, list_tail(&zilog->zl_lwb_list));
2984 		ASSERT3S(lwb->lwb_state, !=, LWB_STATE_ISSUED);
2985 		list_remove(&zilog->zl_lwb_list, lwb);
2986 		zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
2987 		zil_free_lwb(zilog, lwb);
2988 	}
2989 	mutex_exit(&zilog->zl_lock);
2990 }
2991 
2992 static char *suspend_tag = "zil suspending";
2993 
2994 /*
2995  * Suspend an intent log.  While in suspended mode, we still honor
2996  * synchronous semantics, but we rely on txg_wait_synced() to do it.
2997  * On old version pools, we suspend the log briefly when taking a
2998  * snapshot so that it will have an empty intent log.
2999  *
3000  * Long holds are not really intended to be used the way we do here --
3001  * held for such a short time.  A concurrent caller of dsl_dataset_long_held()
3002  * could fail.  Therefore we take pains to only put a long hold if it is
3003  * actually necessary.  Fortunately, it will only be necessary if the
3004  * objset is currently mounted (or the ZVOL equivalent).  In that case it
3005  * will already have a long hold, so we are not really making things any worse.
3006  *
3007  * Ideally, we would locate the existing long-holder (i.e. the zfsvfs_t or
3008  * zvol_state_t), and use their mechanism to prevent their hold from being
3009  * dropped (e.g. VFS_HOLD()).  However, that would be even more pain for
3010  * very little gain.
3011  *
3012  * if cookiep == NULL, this does both the suspend & resume.
3013  * Otherwise, it returns with the dataset "long held", and the cookie
3014  * should be passed into zil_resume().
3015  */
3016 int
3017 zil_suspend(const char *osname, void **cookiep)
3018 {
3019 	objset_t *os;
3020 	zilog_t *zilog;
3021 	const zil_header_t *zh;
3022 	int error;
3023 
3024 	error = dmu_objset_hold(osname, suspend_tag, &os);
3025 	if (error != 0)
3026 		return (error);
3027 	zilog = dmu_objset_zil(os);
3028 
3029 	mutex_enter(&zilog->zl_lock);
3030 	zh = zilog->zl_header;
3031 
3032 	if (zh->zh_flags & ZIL_REPLAY_NEEDED) {		/* unplayed log */
3033 		mutex_exit(&zilog->zl_lock);
3034 		dmu_objset_rele(os, suspend_tag);
3035 		return (SET_ERROR(EBUSY));
3036 	}
3037 
3038 	/*
3039 	 * Don't put a long hold in the cases where we can avoid it.  This
3040 	 * is when there is no cookie so we are doing a suspend & resume
3041 	 * (i.e. called from zil_vdev_offline()), and there's nothing to do
3042 	 * for the suspend because it's already suspended, or there's no ZIL.
3043 	 */
3044 	if (cookiep == NULL && !zilog->zl_suspending &&
3045 	    (zilog->zl_suspend > 0 || BP_IS_HOLE(&zh->zh_log))) {
3046 		mutex_exit(&zilog->zl_lock);
3047 		dmu_objset_rele(os, suspend_tag);
3048 		return (0);
3049 	}
3050 
3051 	dsl_dataset_long_hold(dmu_objset_ds(os), suspend_tag);
3052 	dsl_pool_rele(dmu_objset_pool(os), suspend_tag);
3053 
3054 	zilog->zl_suspend++;
3055 
3056 	if (zilog->zl_suspend > 1) {
3057 		/*
3058 		 * Someone else is already suspending it.
3059 		 * Just wait for them to finish.
3060 		 */
3061 
3062 		while (zilog->zl_suspending)
3063 			cv_wait(&zilog->zl_cv_suspend, &zilog->zl_lock);
3064 		mutex_exit(&zilog->zl_lock);
3065 
3066 		if (cookiep == NULL)
3067 			zil_resume(os);
3068 		else
3069 			*cookiep = os;
3070 		return (0);
3071 	}
3072 
3073 	/*
3074 	 * If there is no pointer to an on-disk block, this ZIL must not
3075 	 * be active (e.g. filesystem not mounted), so there's nothing
3076 	 * to clean up.
3077 	 */
3078 	if (BP_IS_HOLE(&zh->zh_log)) {
3079 		ASSERT(cookiep != NULL); /* fast path already handled */
3080 
3081 		*cookiep = os;
3082 		mutex_exit(&zilog->zl_lock);
3083 		return (0);
3084 	}
3085 
3086 	zilog->zl_suspending = B_TRUE;
3087 	mutex_exit(&zilog->zl_lock);
3088 
3089 	/*
3090 	 * We need to use zil_commit_impl to ensure we wait for all
3091 	 * LWB_STATE_OPENED and LWB_STATE_ISSUED lwb's to be committed
3092 	 * to disk before proceeding. If we used zil_commit instead, it
3093 	 * would just call txg_wait_synced(), because zl_suspend is set.
3094 	 * txg_wait_synced() doesn't wait for these lwb's to be
3095 	 * LWB_STATE_DONE before returning.
3096 	 */
3097 	zil_commit_impl(zilog, 0);
3098 
3099 	/*
3100 	 * Now that we've ensured all lwb's are LWB_STATE_DONE, we use
3101 	 * txg_wait_synced() to ensure the data from the zilog has
3102 	 * migrated to the main pool before calling zil_destroy().
3103 	 */
3104 	txg_wait_synced(zilog->zl_dmu_pool, 0);
3105 
3106 	zil_destroy(zilog, B_FALSE);
3107 
3108 	mutex_enter(&zilog->zl_lock);
3109 	zilog->zl_suspending = B_FALSE;
3110 	cv_broadcast(&zilog->zl_cv_suspend);
3111 	mutex_exit(&zilog->zl_lock);
3112 
3113 	if (cookiep == NULL)
3114 		zil_resume(os);
3115 	else
3116 		*cookiep = os;
3117 	return (0);
3118 }
3119 
3120 void
3121 zil_resume(void *cookie)
3122 {
3123 	objset_t *os = cookie;
3124 	zilog_t *zilog = dmu_objset_zil(os);
3125 
3126 	mutex_enter(&zilog->zl_lock);
3127 	ASSERT(zilog->zl_suspend != 0);
3128 	zilog->zl_suspend--;
3129 	mutex_exit(&zilog->zl_lock);
3130 	dsl_dataset_long_rele(dmu_objset_ds(os), suspend_tag);
3131 	dsl_dataset_rele(dmu_objset_ds(os), suspend_tag);
3132 }
3133 
3134 typedef struct zil_replay_arg {
3135 	zil_replay_func_t **zr_replay;
3136 	void		*zr_arg;
3137 	boolean_t	zr_byteswap;
3138 	char		*zr_lr;
3139 } zil_replay_arg_t;
3140 
3141 static int
3142 zil_replay_error(zilog_t *zilog, lr_t *lr, int error)
3143 {
3144 	char name[ZFS_MAX_DATASET_NAME_LEN];
3145 
3146 	zilog->zl_replaying_seq--;	/* didn't actually replay this one */
3147 
3148 	dmu_objset_name(zilog->zl_os, name);
3149 
3150 	cmn_err(CE_WARN, "ZFS replay transaction error %d, "
3151 	    "dataset %s, seq 0x%llx, txtype %llu %s\n", error, name,
3152 	    (u_longlong_t)lr->lrc_seq,
3153 	    (u_longlong_t)(lr->lrc_txtype & ~TX_CI),
3154 	    (lr->lrc_txtype & TX_CI) ? "CI" : "");
3155 
3156 	return (error);
3157 }
3158 
3159 static int
3160 zil_replay_log_record(zilog_t *zilog, lr_t *lr, void *zra, uint64_t claim_txg)
3161 {
3162 	zil_replay_arg_t *zr = zra;
3163 	const zil_header_t *zh = zilog->zl_header;
3164 	uint64_t reclen = lr->lrc_reclen;
3165 	uint64_t txtype = lr->lrc_txtype;
3166 	int error = 0;
3167 
3168 	zilog->zl_replaying_seq = lr->lrc_seq;
3169 
3170 	if (lr->lrc_seq <= zh->zh_replay_seq)	/* already replayed */
3171 		return (0);
3172 
3173 	if (lr->lrc_txg < claim_txg)		/* already committed */
3174 		return (0);
3175 
3176 	/* Strip case-insensitive bit, still present in log record */
3177 	txtype &= ~TX_CI;
3178 
3179 	if (txtype == 0 || txtype >= TX_MAX_TYPE)
3180 		return (zil_replay_error(zilog, lr, EINVAL));
3181 
3182 	/*
3183 	 * If this record type can be logged out of order, the object
3184 	 * (lr_foid) may no longer exist.  That's legitimate, not an error.
3185 	 */
3186 	if (TX_OOO(txtype)) {
3187 		error = dmu_object_info(zilog->zl_os,
3188 		    ((lr_ooo_t *)lr)->lr_foid, NULL);
3189 		if (error == ENOENT || error == EEXIST)
3190 			return (0);
3191 	}
3192 
3193 	/*
3194 	 * Make a copy of the data so we can revise and extend it.
3195 	 */
3196 	bcopy(lr, zr->zr_lr, reclen);
3197 
3198 	/*
3199 	 * If this is a TX_WRITE with a blkptr, suck in the data.
3200 	 */
3201 	if (txtype == TX_WRITE && reclen == sizeof (lr_write_t)) {
3202 		error = zil_read_log_data(zilog, (lr_write_t *)lr,
3203 		    zr->zr_lr + reclen);
3204 		if (error != 0)
3205 			return (zil_replay_error(zilog, lr, error));
3206 	}
3207 
3208 	/*
3209 	 * The log block containing this lr may have been byteswapped
3210 	 * so that we can easily examine common fields like lrc_txtype.
3211 	 * However, the log is a mix of different record types, and only the
3212 	 * replay vectors know how to byteswap their records.  Therefore, if
3213 	 * the lr was byteswapped, undo it before invoking the replay vector.
3214 	 */
3215 	if (zr->zr_byteswap)
3216 		byteswap_uint64_array(zr->zr_lr, reclen);
3217 
3218 	/*
3219 	 * We must now do two things atomically: replay this log record,
3220 	 * and update the log header sequence number to reflect the fact that
3221 	 * we did so. At the end of each replay function the sequence number
3222 	 * is updated if we are in replay mode.
3223 	 */
3224 	error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, zr->zr_byteswap);
3225 	if (error != 0) {
3226 		/*
3227 		 * The DMU's dnode layer doesn't see removes until the txg
3228 		 * commits, so a subsequent claim can spuriously fail with
3229 		 * EEXIST. So if we receive any error we try syncing out
3230 		 * any removes then retry the transaction.  Note that we
3231 		 * specify B_FALSE for byteswap now, so we don't do it twice.
3232 		 */
3233 		txg_wait_synced(spa_get_dsl(zilog->zl_spa), 0);
3234 		error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, B_FALSE);
3235 		if (error != 0)
3236 			return (zil_replay_error(zilog, lr, error));
3237 	}
3238 	return (0);
3239 }
3240 
3241 /* ARGSUSED */
3242 static int
3243 zil_incr_blks(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
3244 {
3245 	zilog->zl_replay_blks++;
3246 
3247 	return (0);
3248 }
3249 
3250 /*
3251  * If this dataset has a non-empty intent log, replay it and destroy it.
3252  */
3253 void
3254 zil_replay(objset_t *os, void *arg, zil_replay_func_t *replay_func[TX_MAX_TYPE])
3255 {
3256 	zilog_t *zilog = dmu_objset_zil(os);
3257 	const zil_header_t *zh = zilog->zl_header;
3258 	zil_replay_arg_t zr;
3259 
3260 	if ((zh->zh_flags & ZIL_REPLAY_NEEDED) == 0) {
3261 		zil_destroy(zilog, B_TRUE);
3262 		return;
3263 	}
3264 
3265 	zr.zr_replay = replay_func;
3266 	zr.zr_arg = arg;
3267 	zr.zr_byteswap = BP_SHOULD_BYTESWAP(&zh->zh_log);
3268 	zr.zr_lr = kmem_alloc(2 * SPA_MAXBLOCKSIZE, KM_SLEEP);
3269 
3270 	/*
3271 	 * Wait for in-progress removes to sync before starting replay.
3272 	 */
3273 	txg_wait_synced(zilog->zl_dmu_pool, 0);
3274 
3275 	zilog->zl_replay = B_TRUE;
3276 	zilog->zl_replay_time = ddi_get_lbolt();
3277 	ASSERT(zilog->zl_replay_blks == 0);
3278 	(void) zil_parse(zilog, zil_incr_blks, zil_replay_log_record, &zr,
3279 	    zh->zh_claim_txg);
3280 	kmem_free(zr.zr_lr, 2 * SPA_MAXBLOCKSIZE);
3281 
3282 	zil_destroy(zilog, B_FALSE);
3283 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
3284 	zilog->zl_replay = B_FALSE;
3285 }
3286 
3287 boolean_t
3288 zil_replaying(zilog_t *zilog, dmu_tx_t *tx)
3289 {
3290 	if (zilog->zl_sync == ZFS_SYNC_DISABLED)
3291 		return (B_TRUE);
3292 
3293 	if (zilog->zl_replay) {
3294 		dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
3295 		zilog->zl_replayed_seq[dmu_tx_get_txg(tx) & TXG_MASK] =
3296 		    zilog->zl_replaying_seq;
3297 		return (B_TRUE);
3298 	}
3299 
3300 	return (B_FALSE);
3301 }
3302 
3303 /* ARGSUSED */
3304 int
3305 zil_reset(const char *osname, void *arg)
3306 {
3307 	int error;
3308 
3309 	error = zil_suspend(osname, NULL);
3310 	if (error != 0)
3311 		return (SET_ERROR(EEXIST));
3312 	return (0);
3313 }
3314