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 * Portions Copyright 2011 Martin Matuska
24 * Copyright (c) 2012, 2017 by Delphix. All rights reserved.
25 */
26
27#include <sys/zfs_context.h>
28#include <sys/txg_impl.h>
29#include <sys/dmu_impl.h>
30#include <sys/dmu_tx.h>
31#include <sys/dsl_pool.h>
32#include <sys/dsl_scan.h>
33#include <sys/zil.h>
34#include <sys/callb.h>
35
36/*
37 * ZFS Transaction Groups
38 * ----------------------
39 *
40 * ZFS transaction groups are, as the name implies, groups of transactions
41 * that act on persistent state. ZFS asserts consistency at the granularity of
42 * these transaction groups. Each successive transaction group (txg) is
43 * assigned a 64-bit consecutive identifier. There are three active
44 * transaction group states: open, quiescing, or syncing. At any given time,
45 * there may be an active txg associated with each state; each active txg may
46 * either be processing, or blocked waiting to enter the next state. There may
47 * be up to three active txgs, and there is always a txg in the open state
48 * (though it may be blocked waiting to enter the quiescing state). In broad
49 * strokes, transactions -- operations that change in-memory structures -- are
50 * accepted into the txg in the open state, and are completed while the txg is
51 * in the open or quiescing states. The accumulated changes are written to
52 * disk in the syncing state.
53 *
54 * Open
55 *
56 * When a new txg becomes active, it first enters the open state. New
57 * transactions -- updates to in-memory structures -- are assigned to the
58 * currently open txg. There is always a txg in the open state so that ZFS can
59 * accept new changes (though the txg may refuse new changes if it has hit
60 * some limit). ZFS advances the open txg to the next state for a variety of
61 * reasons such as it hitting a time or size threshold, or the execution of an
62 * administrative action that must be completed in the syncing state.
63 *
64 * Quiescing
65 *
66 * After a txg exits the open state, it enters the quiescing state. The
67 * quiescing state is intended to provide a buffer between accepting new
68 * transactions in the open state and writing them out to stable storage in
69 * the syncing state. While quiescing, transactions can continue their
70 * operation without delaying either of the other states. Typically, a txg is
71 * in the quiescing state very briefly since the operations are bounded by
72 * software latencies rather than, say, slower I/O latencies. After all
73 * transactions complete, the txg is ready to enter the next state.
74 *
75 * Syncing
76 *
77 * In the syncing state, the in-memory state built up during the open and (to
78 * a lesser degree) the quiescing states is written to stable storage. The
79 * process of writing out modified data can, in turn modify more data. For
80 * example when we write new blocks, we need to allocate space for them; those
81 * allocations modify metadata (space maps)... which themselves must be
82 * written to stable storage. During the sync state, ZFS iterates, writing out
83 * data until it converges and all in-memory changes have been written out.
84 * The first such pass is the largest as it encompasses all the modified user
85 * data (as opposed to filesystem metadata). Subsequent passes typically have
86 * far less data to write as they consist exclusively of filesystem metadata.
87 *
88 * To ensure convergence, after a certain number of passes ZFS begins
89 * overwriting locations on stable storage that had been allocated earlier in
90 * the syncing state (and subsequently freed). ZFS usually allocates new
91 * blocks to optimize for large, continuous, writes. For the syncing state to
92 * converge however it must complete a pass where no new blocks are allocated
93 * since each allocation requires a modification of persistent metadata.
94 * Further, to hasten convergence, after a prescribed number of passes, ZFS
95 * also defers frees, and stops compressing.
96 *
97 * In addition to writing out user data, we must also execute synctasks during
98 * the syncing context. A synctask is the mechanism by which some
99 * administrative activities work such as creating and destroying snapshots or
100 * datasets. Note that when a synctask is initiated it enters the open txg,
101 * and ZFS then pushes that txg as quickly as possible to completion of the
102 * syncing state in order to reduce the latency of the administrative
103 * activity. To complete the syncing state, ZFS writes out a new uberblock,
104 * the root of the tree of blocks that comprise all state stored on the ZFS
105 * pool. Finally, if there is a quiesced txg waiting, we signal that it can
106 * now transition to the syncing state.
107 */
108
109static void txg_sync_thread(dsl_pool_t *dp);
110static void txg_quiesce_thread(dsl_pool_t *dp);
111
112int zfs_txg_timeout = 5;	/* max seconds worth of delta per txg */
113
114/*
115 * Prepare the txg subsystem.
116 */
117void
118txg_init(dsl_pool_t *dp, uint64_t txg)
119{
120	tx_state_t *tx = &dp->dp_tx;
121	int c;
122	bzero(tx, sizeof (tx_state_t));
123
124	tx->tx_cpu = kmem_zalloc(max_ncpus * sizeof (tx_cpu_t), KM_SLEEP);
125
126	for (c = 0; c < max_ncpus; c++) {
127		int i;
128
129		mutex_init(&tx->tx_cpu[c].tc_lock, NULL, MUTEX_DEFAULT, NULL);
130		mutex_init(&tx->tx_cpu[c].tc_open_lock, NULL, MUTEX_DEFAULT,
131		    NULL);
132		for (i = 0; i < TXG_SIZE; i++) {
133			cv_init(&tx->tx_cpu[c].tc_cv[i], NULL, CV_DEFAULT,
134			    NULL);
135			list_create(&tx->tx_cpu[c].tc_callbacks[i],
136			    sizeof (dmu_tx_callback_t),
137			    offsetof(dmu_tx_callback_t, dcb_node));
138		}
139	}
140
141	mutex_init(&tx->tx_sync_lock, NULL, MUTEX_DEFAULT, NULL);
142
143	cv_init(&tx->tx_sync_more_cv, NULL, CV_DEFAULT, NULL);
144	cv_init(&tx->tx_sync_done_cv, NULL, CV_DEFAULT, NULL);
145	cv_init(&tx->tx_quiesce_more_cv, NULL, CV_DEFAULT, NULL);
146	cv_init(&tx->tx_quiesce_done_cv, NULL, CV_DEFAULT, NULL);
147	cv_init(&tx->tx_exit_cv, NULL, CV_DEFAULT, NULL);
148
149	tx->tx_open_txg = txg;
150}
151
152/*
153 * Close down the txg subsystem.
154 */
155void
156txg_fini(dsl_pool_t *dp)
157{
158	tx_state_t *tx = &dp->dp_tx;
159	int c;
160
161	ASSERT(tx->tx_threads == 0);
162
163	mutex_destroy(&tx->tx_sync_lock);
164
165	cv_destroy(&tx->tx_sync_more_cv);
166	cv_destroy(&tx->tx_sync_done_cv);
167	cv_destroy(&tx->tx_quiesce_more_cv);
168	cv_destroy(&tx->tx_quiesce_done_cv);
169	cv_destroy(&tx->tx_exit_cv);
170
171	for (c = 0; c < max_ncpus; c++) {
172		int i;
173
174		mutex_destroy(&tx->tx_cpu[c].tc_open_lock);
175		mutex_destroy(&tx->tx_cpu[c].tc_lock);
176		for (i = 0; i < TXG_SIZE; i++) {
177			cv_destroy(&tx->tx_cpu[c].tc_cv[i]);
178			list_destroy(&tx->tx_cpu[c].tc_callbacks[i]);
179		}
180	}
181
182	if (tx->tx_commit_cb_taskq != NULL)
183		taskq_destroy(tx->tx_commit_cb_taskq);
184
185	kmem_free(tx->tx_cpu, max_ncpus * sizeof (tx_cpu_t));
186
187	bzero(tx, sizeof (tx_state_t));
188}
189
190/*
191 * Start syncing transaction groups.
192 */
193void
194txg_sync_start(dsl_pool_t *dp)
195{
196	tx_state_t *tx = &dp->dp_tx;
197
198	mutex_enter(&tx->tx_sync_lock);
199
200	dprintf("pool %p\n", dp);
201
202	ASSERT(tx->tx_threads == 0);
203
204	tx->tx_threads = 2;
205
206	tx->tx_quiesce_thread = thread_create(NULL, 0, txg_quiesce_thread,
207	    dp, 0, &p0, TS_RUN, minclsyspri);
208
209	/*
210	 * The sync thread can need a larger-than-default stack size on
211	 * 32-bit x86.  This is due in part to nested pools and
212	 * scrub_visitbp() recursion.
213	 */
214	tx->tx_sync_thread = thread_create(NULL, 32<<10, txg_sync_thread,
215	    dp, 0, &p0, TS_RUN, minclsyspri);
216
217	mutex_exit(&tx->tx_sync_lock);
218}
219
220static void
221txg_thread_enter(tx_state_t *tx, callb_cpr_t *cpr)
222{
223	CALLB_CPR_INIT(cpr, &tx->tx_sync_lock, callb_generic_cpr, FTAG);
224	mutex_enter(&tx->tx_sync_lock);
225}
226
227static void
228txg_thread_exit(tx_state_t *tx, callb_cpr_t *cpr, kthread_t **tpp)
229{
230	ASSERT(*tpp != NULL);
231	*tpp = NULL;
232	tx->tx_threads--;
233	cv_broadcast(&tx->tx_exit_cv);
234	CALLB_CPR_EXIT(cpr);		/* drops &tx->tx_sync_lock */
235	thread_exit();
236}
237
238static void
239txg_thread_wait(tx_state_t *tx, callb_cpr_t *cpr, kcondvar_t *cv, clock_t time)
240{
241	CALLB_CPR_SAFE_BEGIN(cpr);
242
243	if (time)
244		(void) cv_timedwait(cv, &tx->tx_sync_lock,
245		    ddi_get_lbolt() + time);
246	else
247		cv_wait(cv, &tx->tx_sync_lock);
248
249	CALLB_CPR_SAFE_END(cpr, &tx->tx_sync_lock);
250}
251
252/*
253 * Stop syncing transaction groups.
254 */
255void
256txg_sync_stop(dsl_pool_t *dp)
257{
258	tx_state_t *tx = &dp->dp_tx;
259
260	dprintf("pool %p\n", dp);
261	/*
262	 * Finish off any work in progress.
263	 */
264	ASSERT(tx->tx_threads == 2);
265
266	/*
267	 * We need to ensure that we've vacated the deferred space_maps.
268	 */
269	txg_wait_synced(dp, tx->tx_open_txg + TXG_DEFER_SIZE);
270
271	/*
272	 * Wake all sync threads and wait for them to die.
273	 */
274	mutex_enter(&tx->tx_sync_lock);
275
276	ASSERT(tx->tx_threads == 2);
277
278	tx->tx_exiting = 1;
279
280	cv_broadcast(&tx->tx_quiesce_more_cv);
281	cv_broadcast(&tx->tx_quiesce_done_cv);
282	cv_broadcast(&tx->tx_sync_more_cv);
283
284	while (tx->tx_threads != 0)
285		cv_wait(&tx->tx_exit_cv, &tx->tx_sync_lock);
286
287	tx->tx_exiting = 0;
288
289	mutex_exit(&tx->tx_sync_lock);
290}
291
292uint64_t
293txg_hold_open(dsl_pool_t *dp, txg_handle_t *th)
294{
295	tx_state_t *tx = &dp->dp_tx;
296	tx_cpu_t *tc = &tx->tx_cpu[CPU_SEQID];
297	uint64_t txg;
298
299	mutex_enter(&tc->tc_open_lock);
300	txg = tx->tx_open_txg;
301
302	mutex_enter(&tc->tc_lock);
303	tc->tc_count[txg & TXG_MASK]++;
304	mutex_exit(&tc->tc_lock);
305
306	th->th_cpu = tc;
307	th->th_txg = txg;
308
309	return (txg);
310}
311
312void
313txg_rele_to_quiesce(txg_handle_t *th)
314{
315	tx_cpu_t *tc = th->th_cpu;
316
317	ASSERT(!MUTEX_HELD(&tc->tc_lock));
318	mutex_exit(&tc->tc_open_lock);
319}
320
321void
322txg_register_callbacks(txg_handle_t *th, list_t *tx_callbacks)
323{
324	tx_cpu_t *tc = th->th_cpu;
325	int g = th->th_txg & TXG_MASK;
326
327	mutex_enter(&tc->tc_lock);
328	list_move_tail(&tc->tc_callbacks[g], tx_callbacks);
329	mutex_exit(&tc->tc_lock);
330}
331
332void
333txg_rele_to_sync(txg_handle_t *th)
334{
335	tx_cpu_t *tc = th->th_cpu;
336	int g = th->th_txg & TXG_MASK;
337
338	mutex_enter(&tc->tc_lock);
339	ASSERT(tc->tc_count[g] != 0);
340	if (--tc->tc_count[g] == 0)
341		cv_broadcast(&tc->tc_cv[g]);
342	mutex_exit(&tc->tc_lock);
343
344	th->th_cpu = NULL;	/* defensive */
345}
346
347/*
348 * Blocks until all transactions in the group are committed.
349 *
350 * On return, the transaction group has reached a stable state in which it can
351 * then be passed off to the syncing context.
352 */
353static void
354txg_quiesce(dsl_pool_t *dp, uint64_t txg)
355{
356	tx_state_t *tx = &dp->dp_tx;
357	int g = txg & TXG_MASK;
358	int c;
359
360	/*
361	 * Grab all tc_open_locks so nobody else can get into this txg.
362	 */
363	for (c = 0; c < max_ncpus; c++)
364		mutex_enter(&tx->tx_cpu[c].tc_open_lock);
365
366	ASSERT(txg == tx->tx_open_txg);
367	tx->tx_open_txg++;
368	tx->tx_open_time = gethrtime();
369
370	DTRACE_PROBE2(txg__quiescing, dsl_pool_t *, dp, uint64_t, txg);
371	DTRACE_PROBE2(txg__opened, dsl_pool_t *, dp, uint64_t, tx->tx_open_txg);
372
373	/*
374	 * Now that we've incremented tx_open_txg, we can let threads
375	 * enter the next transaction group.
376	 */
377	for (c = 0; c < max_ncpus; c++)
378		mutex_exit(&tx->tx_cpu[c].tc_open_lock);
379
380	/*
381	 * Quiesce the transaction group by waiting for everyone to txg_exit().
382	 */
383	for (c = 0; c < max_ncpus; c++) {
384		tx_cpu_t *tc = &tx->tx_cpu[c];
385		mutex_enter(&tc->tc_lock);
386		while (tc->tc_count[g] != 0)
387			cv_wait(&tc->tc_cv[g], &tc->tc_lock);
388		mutex_exit(&tc->tc_lock);
389	}
390}
391
392static void
393txg_do_callbacks(list_t *cb_list)
394{
395	dmu_tx_do_callbacks(cb_list, 0);
396
397	list_destroy(cb_list);
398
399	kmem_free(cb_list, sizeof (list_t));
400}
401
402/*
403 * Dispatch the commit callbacks registered on this txg to worker threads.
404 *
405 * If no callbacks are registered for a given TXG, nothing happens.
406 * This function creates a taskq for the associated pool, if needed.
407 */
408static void
409txg_dispatch_callbacks(dsl_pool_t *dp, uint64_t txg)
410{
411	int c;
412	tx_state_t *tx = &dp->dp_tx;
413	list_t *cb_list;
414
415	for (c = 0; c < max_ncpus; c++) {
416		tx_cpu_t *tc = &tx->tx_cpu[c];
417		/*
418		 * No need to lock tx_cpu_t at this point, since this can
419		 * only be called once a txg has been synced.
420		 */
421
422		int g = txg & TXG_MASK;
423
424		if (list_is_empty(&tc->tc_callbacks[g]))
425			continue;
426
427		if (tx->tx_commit_cb_taskq == NULL) {
428			/*
429			 * Commit callback taskq hasn't been created yet.
430			 */
431			tx->tx_commit_cb_taskq = taskq_create("tx_commit_cb",
432			    max_ncpus, minclsyspri, max_ncpus, max_ncpus * 2,
433			    TASKQ_PREPOPULATE);
434		}
435
436		cb_list = kmem_alloc(sizeof (list_t), KM_SLEEP);
437		list_create(cb_list, sizeof (dmu_tx_callback_t),
438		    offsetof(dmu_tx_callback_t, dcb_node));
439
440		list_move_tail(cb_list, &tc->tc_callbacks[g]);
441
442		(void) taskq_dispatch(tx->tx_commit_cb_taskq, (task_func_t *)
443		    txg_do_callbacks, cb_list, TQ_SLEEP);
444	}
445}
446
447static void
448txg_sync_thread(dsl_pool_t *dp)
449{
450	spa_t *spa = dp->dp_spa;
451	tx_state_t *tx = &dp->dp_tx;
452	callb_cpr_t cpr;
453	uint64_t start, delta;
454
455	txg_thread_enter(tx, &cpr);
456
457	start = delta = 0;
458	for (;;) {
459		uint64_t timeout = zfs_txg_timeout * hz;
460		uint64_t timer;
461		uint64_t txg;
462
463		/*
464		 * We sync when we're scanning, there's someone waiting
465		 * on us, or the quiesce thread has handed off a txg to
466		 * us, or we have reached our timeout.
467		 */
468		timer = (delta >= timeout ? 0 : timeout - delta);
469		while (!dsl_scan_active(dp->dp_scan) &&
470		    !tx->tx_exiting && timer > 0 &&
471		    tx->tx_synced_txg >= tx->tx_sync_txg_waiting &&
472		    tx->tx_quiesced_txg == 0 &&
473		    dp->dp_dirty_total < zfs_dirty_data_sync) {
474			dprintf("waiting; tx_synced=%llu waiting=%llu dp=%p\n",
475			    tx->tx_synced_txg, tx->tx_sync_txg_waiting, dp);
476			txg_thread_wait(tx, &cpr, &tx->tx_sync_more_cv, timer);
477			delta = ddi_get_lbolt() - start;
478			timer = (delta > timeout ? 0 : timeout - delta);
479		}
480
481		/*
482		 * Wait until the quiesce thread hands off a txg to us,
483		 * prompting it to do so if necessary.
484		 */
485		while (!tx->tx_exiting && tx->tx_quiesced_txg == 0) {
486			if (tx->tx_quiesce_txg_waiting < tx->tx_open_txg+1)
487				tx->tx_quiesce_txg_waiting = tx->tx_open_txg+1;
488			cv_broadcast(&tx->tx_quiesce_more_cv);
489			txg_thread_wait(tx, &cpr, &tx->tx_quiesce_done_cv, 0);
490		}
491
492		if (tx->tx_exiting)
493			txg_thread_exit(tx, &cpr, &tx->tx_sync_thread);
494
495		/*
496		 * Consume the quiesced txg which has been handed off to
497		 * us.  This may cause the quiescing thread to now be
498		 * able to quiesce another txg, so we must signal it.
499		 */
500		txg = tx->tx_quiesced_txg;
501		tx->tx_quiesced_txg = 0;
502		tx->tx_syncing_txg = txg;
503		DTRACE_PROBE2(txg__syncing, dsl_pool_t *, dp, uint64_t, txg);
504		cv_broadcast(&tx->tx_quiesce_more_cv);
505
506		dprintf("txg=%llu quiesce_txg=%llu sync_txg=%llu\n",
507		    txg, tx->tx_quiesce_txg_waiting, tx->tx_sync_txg_waiting);
508		mutex_exit(&tx->tx_sync_lock);
509
510		start = ddi_get_lbolt();
511		spa_sync(spa, txg);
512		delta = ddi_get_lbolt() - start;
513
514		mutex_enter(&tx->tx_sync_lock);
515		tx->tx_synced_txg = txg;
516		tx->tx_syncing_txg = 0;
517		DTRACE_PROBE2(txg__synced, dsl_pool_t *, dp, uint64_t, txg);
518		cv_broadcast(&tx->tx_sync_done_cv);
519
520		/*
521		 * Dispatch commit callbacks to worker threads.
522		 */
523		txg_dispatch_callbacks(dp, txg);
524	}
525}
526
527static void
528txg_quiesce_thread(dsl_pool_t *dp)
529{
530	tx_state_t *tx = &dp->dp_tx;
531	callb_cpr_t cpr;
532
533	txg_thread_enter(tx, &cpr);
534
535	for (;;) {
536		uint64_t txg;
537
538		/*
539		 * We quiesce when there's someone waiting on us.
540		 * However, we can only have one txg in "quiescing" or
541		 * "quiesced, waiting to sync" state.  So we wait until
542		 * the "quiesced, waiting to sync" txg has been consumed
543		 * by the sync thread.
544		 */
545		while (!tx->tx_exiting &&
546		    (tx->tx_open_txg >= tx->tx_quiesce_txg_waiting ||
547		    tx->tx_quiesced_txg != 0))
548			txg_thread_wait(tx, &cpr, &tx->tx_quiesce_more_cv, 0);
549
550		if (tx->tx_exiting)
551			txg_thread_exit(tx, &cpr, &tx->tx_quiesce_thread);
552
553		txg = tx->tx_open_txg;
554		dprintf("txg=%llu quiesce_txg=%llu sync_txg=%llu\n",
555		    txg, tx->tx_quiesce_txg_waiting,
556		    tx->tx_sync_txg_waiting);
557		mutex_exit(&tx->tx_sync_lock);
558		txg_quiesce(dp, txg);
559		mutex_enter(&tx->tx_sync_lock);
560
561		/*
562		 * Hand this txg off to the sync thread.
563		 */
564		dprintf("quiesce done, handing off txg %llu\n", txg);
565		tx->tx_quiesced_txg = txg;
566		DTRACE_PROBE2(txg__quiesced, dsl_pool_t *, dp, uint64_t, txg);
567		cv_broadcast(&tx->tx_sync_more_cv);
568		cv_broadcast(&tx->tx_quiesce_done_cv);
569	}
570}
571
572/*
573 * Delay this thread by delay nanoseconds if we are still in the open
574 * transaction group and there is already a waiting txg quiescing or quiesced.
575 * Abort the delay if this txg stalls or enters the quiescing state.
576 */
577void
578txg_delay(dsl_pool_t *dp, uint64_t txg, hrtime_t delay, hrtime_t resolution)
579{
580	tx_state_t *tx = &dp->dp_tx;
581	hrtime_t start = gethrtime();
582
583	/* don't delay if this txg could transition to quiescing immediately */
584	if (tx->tx_open_txg > txg ||
585	    tx->tx_syncing_txg == txg-1 || tx->tx_synced_txg == txg-1)
586		return;
587
588	mutex_enter(&tx->tx_sync_lock);
589	if (tx->tx_open_txg > txg || tx->tx_synced_txg == txg-1) {
590		mutex_exit(&tx->tx_sync_lock);
591		return;
592	}
593
594	while (gethrtime() - start < delay &&
595	    tx->tx_syncing_txg < txg-1 && !txg_stalled(dp)) {
596		(void) cv_timedwait_hires(&tx->tx_quiesce_more_cv,
597		    &tx->tx_sync_lock, delay, resolution, 0);
598	}
599
600	mutex_exit(&tx->tx_sync_lock);
601}
602
603void
604txg_wait_synced(dsl_pool_t *dp, uint64_t txg)
605{
606	tx_state_t *tx = &dp->dp_tx;
607
608	ASSERT(!dsl_pool_config_held(dp));
609
610	mutex_enter(&tx->tx_sync_lock);
611	ASSERT(tx->tx_threads == 2);
612	if (txg == 0)
613		txg = tx->tx_open_txg + TXG_DEFER_SIZE;
614	if (tx->tx_sync_txg_waiting < txg)
615		tx->tx_sync_txg_waiting = txg;
616	dprintf("txg=%llu quiesce_txg=%llu sync_txg=%llu\n",
617	    txg, tx->tx_quiesce_txg_waiting, tx->tx_sync_txg_waiting);
618	while (tx->tx_synced_txg < txg) {
619		dprintf("broadcasting sync more "
620		    "tx_synced=%llu waiting=%llu dp=%p\n",
621		    tx->tx_synced_txg, tx->tx_sync_txg_waiting, dp);
622		cv_broadcast(&tx->tx_sync_more_cv);
623		cv_wait(&tx->tx_sync_done_cv, &tx->tx_sync_lock);
624	}
625	mutex_exit(&tx->tx_sync_lock);
626}
627
628void
629txg_wait_open(dsl_pool_t *dp, uint64_t txg)
630{
631	tx_state_t *tx = &dp->dp_tx;
632
633	ASSERT(!dsl_pool_config_held(dp));
634
635	mutex_enter(&tx->tx_sync_lock);
636	ASSERT(tx->tx_threads == 2);
637	if (txg == 0)
638		txg = tx->tx_open_txg + 1;
639	if (tx->tx_quiesce_txg_waiting < txg)
640		tx->tx_quiesce_txg_waiting = txg;
641	dprintf("txg=%llu quiesce_txg=%llu sync_txg=%llu\n",
642	    txg, tx->tx_quiesce_txg_waiting, tx->tx_sync_txg_waiting);
643	while (tx->tx_open_txg < txg) {
644		cv_broadcast(&tx->tx_quiesce_more_cv);
645		cv_wait(&tx->tx_quiesce_done_cv, &tx->tx_sync_lock);
646	}
647	mutex_exit(&tx->tx_sync_lock);
648}
649
650/*
651 * If there isn't a txg syncing or in the pipeline, push another txg through
652 * the pipeline by queiscing the open txg.
653 */
654void
655txg_kick(dsl_pool_t *dp)
656{
657	tx_state_t *tx = &dp->dp_tx;
658
659	ASSERT(!dsl_pool_config_held(dp));
660
661	mutex_enter(&tx->tx_sync_lock);
662	if (tx->tx_syncing_txg == 0 &&
663	    tx->tx_quiesce_txg_waiting <= tx->tx_open_txg &&
664	    tx->tx_sync_txg_waiting <= tx->tx_synced_txg &&
665	    tx->tx_quiesced_txg <= tx->tx_synced_txg) {
666		tx->tx_quiesce_txg_waiting = tx->tx_open_txg + 1;
667		cv_broadcast(&tx->tx_quiesce_more_cv);
668	}
669	mutex_exit(&tx->tx_sync_lock);
670}
671
672boolean_t
673txg_stalled(dsl_pool_t *dp)
674{
675	tx_state_t *tx = &dp->dp_tx;
676	return (tx->tx_quiesce_txg_waiting > tx->tx_open_txg);
677}
678
679boolean_t
680txg_sync_waiting(dsl_pool_t *dp)
681{
682	tx_state_t *tx = &dp->dp_tx;
683
684	return (tx->tx_syncing_txg <= tx->tx_sync_txg_waiting ||
685	    tx->tx_quiesced_txg != 0);
686}
687
688/*
689 * Verify that this txg is active (open, quiescing, syncing).  Non-active
690 * txg's should not be manipulated.
691 */
692void
693txg_verify(spa_t *spa, uint64_t txg)
694{
695	dsl_pool_t *dp = spa_get_dsl(spa);
696	if (txg <= TXG_INITIAL || txg == ZILTEST_TXG)
697		return;
698	ASSERT3U(txg, <=, dp->dp_tx.tx_open_txg);
699	ASSERT3U(txg, >=, dp->dp_tx.tx_synced_txg);
700	ASSERT3U(txg, >=, dp->dp_tx.tx_open_txg - TXG_CONCURRENT_STATES);
701}
702
703/*
704 * Per-txg object lists.
705 */
706void
707txg_list_create(txg_list_t *tl, spa_t *spa, size_t offset)
708{
709	int t;
710
711	mutex_init(&tl->tl_lock, NULL, MUTEX_DEFAULT, NULL);
712
713	tl->tl_offset = offset;
714	tl->tl_spa = spa;
715
716	for (t = 0; t < TXG_SIZE; t++)
717		tl->tl_head[t] = NULL;
718}
719
720void
721txg_list_destroy(txg_list_t *tl)
722{
723	int t;
724
725	for (t = 0; t < TXG_SIZE; t++)
726		ASSERT(txg_list_empty(tl, t));
727
728	mutex_destroy(&tl->tl_lock);
729}
730
731boolean_t
732txg_list_empty(txg_list_t *tl, uint64_t txg)
733{
734	txg_verify(tl->tl_spa, txg);
735	return (tl->tl_head[txg & TXG_MASK] == NULL);
736}
737
738/*
739 * Returns true if all txg lists are empty.
740 *
741 * Warning: this is inherently racy (an item could be added immediately
742 * after this function returns). We don't bother with the lock because
743 * it wouldn't change the semantics.
744 */
745boolean_t
746txg_all_lists_empty(txg_list_t *tl)
747{
748	for (int i = 0; i < TXG_SIZE; i++) {
749		if (!txg_list_empty(tl, i)) {
750			return (B_FALSE);
751		}
752	}
753	return (B_TRUE);
754}
755
756/*
757 * Add an entry to the list (unless it's already on the list).
758 * Returns B_TRUE if it was actually added.
759 */
760boolean_t
761txg_list_add(txg_list_t *tl, void *p, uint64_t txg)
762{
763	int t = txg & TXG_MASK;
764	txg_node_t *tn = (txg_node_t *)((char *)p + tl->tl_offset);
765	boolean_t add;
766
767	txg_verify(tl->tl_spa, txg);
768	mutex_enter(&tl->tl_lock);
769	add = (tn->tn_member[t] == 0);
770	if (add) {
771		tn->tn_member[t] = 1;
772		tn->tn_next[t] = tl->tl_head[t];
773		tl->tl_head[t] = tn;
774	}
775	mutex_exit(&tl->tl_lock);
776
777	return (add);
778}
779
780/*
781 * Add an entry to the end of the list, unless it's already on the list.
782 * (walks list to find end)
783 * Returns B_TRUE if it was actually added.
784 */
785boolean_t
786txg_list_add_tail(txg_list_t *tl, void *p, uint64_t txg)
787{
788	int t = txg & TXG_MASK;
789	txg_node_t *tn = (txg_node_t *)((char *)p + tl->tl_offset);
790	boolean_t add;
791
792	txg_verify(tl->tl_spa, txg);
793	mutex_enter(&tl->tl_lock);
794	add = (tn->tn_member[t] == 0);
795	if (add) {
796		txg_node_t **tp;
797
798		for (tp = &tl->tl_head[t]; *tp != NULL; tp = &(*tp)->tn_next[t])
799			continue;
800
801		tn->tn_member[t] = 1;
802		tn->tn_next[t] = NULL;
803		*tp = tn;
804	}
805	mutex_exit(&tl->tl_lock);
806
807	return (add);
808}
809
810/*
811 * Remove the head of the list and return it.
812 */
813void *
814txg_list_remove(txg_list_t *tl, uint64_t txg)
815{
816	int t = txg & TXG_MASK;
817	txg_node_t *tn;
818	void *p = NULL;
819
820	txg_verify(tl->tl_spa, txg);
821	mutex_enter(&tl->tl_lock);
822	if ((tn = tl->tl_head[t]) != NULL) {
823		p = (char *)tn - tl->tl_offset;
824		tl->tl_head[t] = tn->tn_next[t];
825		tn->tn_next[t] = NULL;
826		tn->tn_member[t] = 0;
827	}
828	mutex_exit(&tl->tl_lock);
829
830	return (p);
831}
832
833/*
834 * Remove a specific item from the list and return it.
835 */
836void *
837txg_list_remove_this(txg_list_t *tl, void *p, uint64_t txg)
838{
839	int t = txg & TXG_MASK;
840	txg_node_t *tn, **tp;
841
842	txg_verify(tl->tl_spa, txg);
843	mutex_enter(&tl->tl_lock);
844
845	for (tp = &tl->tl_head[t]; (tn = *tp) != NULL; tp = &tn->tn_next[t]) {
846		if ((char *)tn - tl->tl_offset == p) {
847			*tp = tn->tn_next[t];
848			tn->tn_next[t] = NULL;
849			tn->tn_member[t] = 0;
850			mutex_exit(&tl->tl_lock);
851			return (p);
852		}
853	}
854
855	mutex_exit(&tl->tl_lock);
856
857	return (NULL);
858}
859
860boolean_t
861txg_list_member(txg_list_t *tl, void *p, uint64_t txg)
862{
863	int t = txg & TXG_MASK;
864	txg_node_t *tn = (txg_node_t *)((char *)p + tl->tl_offset);
865
866	txg_verify(tl->tl_spa, txg);
867	return (tn->tn_member[t] != 0);
868}
869
870/*
871 * Walk a txg list -- only safe if you know it's not changing.
872 */
873void *
874txg_list_head(txg_list_t *tl, uint64_t txg)
875{
876	int t = txg & TXG_MASK;
877	txg_node_t *tn = tl->tl_head[t];
878
879	txg_verify(tl->tl_spa, txg);
880	return (tn == NULL ? NULL : (char *)tn - tl->tl_offset);
881}
882
883void *
884txg_list_next(txg_list_t *tl, void *p, uint64_t txg)
885{
886	int t = txg & TXG_MASK;
887	txg_node_t *tn = (txg_node_t *)((char *)p + tl->tl_offset);
888
889	txg_verify(tl->tl_spa, txg);
890	tn = tn->tn_next[t];
891
892	return (tn == NULL ? NULL : (char *)tn - tl->tl_offset);
893}
894