summaryrefslogtreecommitdiffstats
path: root/fs/jbd2/checkpoint.c
blob: 5247e7ffdcb46d400e10681535a5728ef8006ad8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
/*
 * linux/fs/jbd2/checkpoint.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1999
 *
 * Copyright 1999 Red Hat Software --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Checkpoint routines for the generic filesystem journaling code.
 * Part of the ext2fs journaling system.
 *
 * Checkpointing is the process of ensuring that a section of the log is
 * committed fully to disk, so that that portion of the log can be
 * reused.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <trace/events/jbd2.h>

/*
 * Unlink a buffer from a transaction checkpoint list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink_first(struct journal_head *jh)
{
	transaction_t *transaction = jh->b_cp_transaction;

	jh->b_cpnext->b_cpprev = jh->b_cpprev;
	jh->b_cpprev->b_cpnext = jh->b_cpnext;
	if (transaction->t_checkpoint_list == jh) {
		transaction->t_checkpoint_list = jh->b_cpnext;
		if (transaction->t_checkpoint_list == jh)
			transaction->t_checkpoint_list = NULL;
	}
}

/*
 * Unlink a buffer from a transaction checkpoint(io) list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink(struct journal_head *jh)
{
	transaction_t *transaction = jh->b_cp_transaction;

	__buffer_unlink_first(jh);
	if (transaction->t_checkpoint_io_list == jh) {
		transaction->t_checkpoint_io_list = jh->b_cpnext;
		if (transaction->t_checkpoint_io_list == jh)
			transaction->t_checkpoint_io_list = NULL;
	}
}

/*
 * Move a buffer from the checkpoint list to the checkpoint io list
 *
 * Called with j_list_lock held
 */
static inline void __buffer_relink_io(struct journal_head *jh)
{
	transaction_t *transaction = jh->b_cp_transaction;

	__buffer_unlink_first(jh);

	if (!transaction->t_checkpoint_io_list) {
		jh->b_cpnext = jh->b_cpprev = jh;
	} else {
		jh->b_cpnext = transaction->t_checkpoint_io_list;
		jh->b_cpprev = transaction->t_checkpoint_io_list->b_cpprev;
		jh->b_cpprev->b_cpnext = jh;
		jh->b_cpnext->b_cpprev = jh;
	}
	transaction->t_checkpoint_io_list = jh;
}

/*
 * Try to release a checkpointed buffer from its transaction.
 * Returns 1 if we released it and 2 if we also released the
 * whole transaction.
 *
 * Requires j_list_lock
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
static int __try_to_free_cp_buf(struct journal_head *jh)
{
	int ret = 0;
	struct buffer_head *bh = jh2bh(jh);

	if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
	    !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
		JBUFFER_TRACE(jh, "remove from checkpoint list");
		ret = __jbd2_journal_remove_checkpoint(jh) + 1;
		jbd_unlock_bh_state(bh);
		jbd2_journal_remove_journal_head(bh);
		BUFFER_TRACE(bh, "release");
		__brelse(bh);
	} else {
		jbd_unlock_bh_state(bh);
	}
	return ret;
}

/*
 * __jbd2_log_wait_for_space: wait until there is space in the journal.
 *
 * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 * for a checkpoint to free up some space in the log.
 */
void __jbd2_log_wait_for_space(journal_t *journal)
{
	int nblocks, space_left;
	/* assert_spin_locked(&journal->j_state_lock); */

	nblocks = jbd_space_needed(journal);
	while (__jbd2_log_space_left(journal) < nblocks) {
		if (journal->j_flags & JBD2_ABORT)
			return;
		write_unlock(&journal->j_state_lock);
		mutex_lock(&journal->j_checkpoint_mutex);

		/*
		 * Test again, another process may have checkpointed while we
		 * were waiting for the checkpoint lock. If there are no
		 * transactions ready to be checkpointed, try to recover
		 * journal space by calling cleanup_journal_tail(), and if
		 * that doesn't work, by waiting for the currently committing
		 * transaction to complete.  If there is absolutely no way
		 * to make progress, this is either a BUG or corrupted
		 * filesystem, so abort the journal and leave a stack
		 * trace for forensic evidence.
		 */
		write_lock(&journal->j_state_lock);
		spin_lock(&journal->j_list_lock);
		nblocks = jbd_space_needed(journal);
		space_left = __jbd2_log_space_left(journal);
		if (space_left < nblocks) {
			int chkpt = journal->j_checkpoint_transactions != NULL;
			tid_t tid = 0;

			if (journal->j_committing_transaction)
				tid = journal->j_committing_transaction->t_tid;
			spin_unlock(&journal->j_list_lock);
			write_unlock(&journal->j_state_lock);
			if (chkpt) {
				jbd2_log_do_checkpoint(journal);
			} else if (jbd2_cleanup_journal_tail(journal) == 0) {
				/* We were able to recover space; yay! */
				;
			} else if (tid) {
				jbd2_log_wait_commit(journal, tid);
			} else {
				printk(KERN_ERR "%s: needed %d blocks and "
				       "only had %d space available\n",
				       __func__, nblocks, space_left);
				printk(KERN_ERR "%s: no way to get more "
				       "journal space in %s\n", __func__,
				       journal->j_devname);
				WARN_ON(1);
				jbd2_journal_abort(journal, 0);
			}
			write_lock(&journal->j_state_lock);
		} else {
			spin_unlock(&journal->j_list_lock);
		}
		mutex_unlock(&journal->j_checkpoint_mutex);
	}
}

/*
 * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 * The caller must restart a list walk.  Wait for someone else to run
 * jbd_unlock_bh_state().
 */
static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
	__releases(journal->j_list_lock)
{
	get_bh(bh);
	spin_unlock(&journal->j_list_lock);
	jbd_lock_bh_state(bh);
	jbd_unlock_bh_state(bh);
	put_bh(bh);
}

/*
 * Clean up transaction's list of buffers submitted for io.
 * We wait for any pending IO to complete and remove any clean
 * buffers. Note that we take the buffers in the opposite ordering
 * from the one in which they were submitted for IO.
 *
 * Return 0 on success, and return <0 if some buffers have failed
 * to be written out.
 *
 * Called with j_list_lock held.
 */
static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
{
	struct journal_head *jh;
	struct buffer_head *bh;
	tid_t this_tid;
	int released = 0;
	int ret = 0;

	this_tid = transaction->t_tid;
restart:
	/* Did somebody clean up the transaction in the meanwhile? */
	if (journal->j_checkpoint_transactions != transaction ||
			transaction->t_tid != this_tid)
		return ret;
	while (!released && transaction->t_checkpoint_io_list) {
		jh = transaction->t_checkpoint_io_list;
		bh = jh2bh(jh);
		if (!jbd_trylock_bh_state(bh)) {
			jbd_sync_bh(journal, bh);
			spin_lock(&journal->j_list_lock);
			goto restart;
		}
		if (buffer_locked(bh)) {
			atomic_inc(&bh->b_count);
			spin_unlock(&journal->j_list_lock);
			jbd_unlock_bh_state(bh);
			wait_on_buffer(bh);
			/* the journal_head may have gone by now */
			BUFFER_TRACE(bh, "brelse");
			__brelse(bh);
			spin_lock(&journal->j_list_lock);
			goto restart;
		}
		if (unlikely(buffer_write_io_error(bh)))
			ret = -EIO;

		/*
		 * Now in whatever state the buffer currently is, we know that
		 * it has been written out and so we can drop it from the list
		 */
		released = __jbd2_journal_remove_checkpoint(jh);
		jbd_unlock_bh_state(bh);
		jbd2_journal_remove_journal_head(bh);
		__brelse(bh);
	}

	return ret;
}

static void
__flush_batch(journal_t *journal, int *batch_count)
{
	int i;

	for (i = 0; i < *batch_count; i++)
		write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE);

	for (i = 0; i < *batch_count; i++) {
		struct buffer_head *bh = journal->j_chkpt_bhs[i];
		clear_buffer_jwrite(bh);
		BUFFER_TRACE(bh, "brelse");
		__brelse(bh);
	}
	*batch_count = 0;
}

/*
 * Try to flush one buffer from the checkpoint list to disk.
 *
 * Return 1 if something happened which requires us to abort the current
 * scan of the checkpoint list.  Return <0 if the buffer has failed to
 * be written out.
 *
 * Called with j_list_lock held and drops it if 1 is returned
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
static int __process_buffer(journal_t *journal, struct journal_head *jh,
			    int *batch_count, transaction_t *transaction)
{
	struct buffer_head *bh = jh2bh(jh);
	int ret = 0;

	if (buffer_locked(bh)) {
		atomic_inc(&bh->b_count);
		spin_unlock(&journal->j_list_lock);
		jbd_unlock_bh_state(bh);
		wait_on_buffer(bh);
		/* the journal_head may have gone by now */
		BUFFER_TRACE(bh, "brelse");
		__brelse(bh);
		ret = 1;
	} else if (jh->b_transaction != NULL) {
		transaction_t *t = jh->b_transaction;
		tid_t tid = t->t_tid;

		transaction->t_chp_stats.cs_forced_to_close++;
		spin_unlock(&journal->j_list_lock);
		jbd_unlock_bh_state(bh);
		jbd2_log_start_commit(journal, tid);
		jbd2_log_wait_commit(journal, tid);
		ret = 1;
	} else if (!buffer_dirty(bh)) {
		ret = 1;
		if (unlikely(buffer_write_io_error(bh)))
			ret = -EIO;
		J_ASSERT_JH(jh, !buffer_jbddirty(bh));
		BUFFER_TRACE(bh, "remove from checkpoint");
		__jbd2_journal_remove_checkpoint(jh);
		spin_unlock(&journal->j_list_lock);
		jbd_unlock_bh_state(bh);
		jbd2_journal_remove_journal_head(bh);
		__brelse(bh);
	} else {
		/*
		 * Important: we are about to write the buffer, and
		 * possibly block, while still holding the journal lock.
		 * We cannot afford to let the transaction logic start
		 * messing around with this buffer before we write it to
		 * disk, as that would break recoverability.
		 */
		BUFFER_TRACE(bh, "queue");
		get_bh(bh);
		J_ASSERT_BH(bh, !buffer_jwrite(bh));
		set_buffer_jwrite(bh);
		journal->j_chkpt_bhs[*batch_count] = bh;
		__buffer_relink_io(jh);
		jbd_unlock_bh_state(bh);
		transaction->t_chp_stats.cs_written++;
		(*batch_count)++;
		if (*batch_count == JBD2_NR_BATCH) {
			spin_unlock(&journal->j_list_lock);
			__flush_batch(journal, batch_count);
			ret = 1;
		}
	}
	return ret;
}

/*
 * Perform an actual checkpoint. We take the first transaction on the
 * list of transactions to be checkpointed and send all its buffers
 * to disk. We submit larger chunks of data at once.
 *
 * The journal should be locked before calling this function.
 * Called with j_checkpoint_mutex held.
 */
int jbd2_log_do_checkpoint(journal_t *journal)
{
	transaction_t *transaction;
	tid_t this_tid;
	int result;

	jbd_debug(1, "Start checkpoint\n");

	/*
	 * First thing: if there are any transactions in the log which
	 * don't need checkpointing, just eliminate them from the
	 * journal straight away.
	 */
	result = jbd2_cleanup_journal_tail(journal);
	trace_jbd2_checkpoint(journal, result);
	jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
	if (result <= 0)
		return result;

	/*
	 * OK, we need to start writing disk blocks.  Take one transaction
	 * and write it.
	 */
	result = 0;
	spin_lock(&journal->j_list_lock);
	if (!journal->j_checkpoint_transactions)
		goto out;
	transaction = journal->j_checkpoint_transactions;
	if (transaction->t_chp_stats.cs_chp_time == 0)
		transaction->t_chp_stats.cs_chp_time = jiffies;
	this_tid = transaction->t_tid;
restart:
	/*
	 * If someone cleaned up this transaction while we slept, we're
	 * done (maybe it's a new transaction, but it fell at the same
	 * address).
	 */
	if (journal->j_checkpoint_transactions == transaction &&
			transaction->t_tid == this_tid) {
		int batch_count = 0;
		struct journal_head *jh;
		int retry = 0, err;

		while (!retry && transaction->t_checkpoint_list) {
			struct buffer_head *bh;

			jh = transaction->t_checkpoint_list;
			bh = jh2bh(jh);
			if (!jbd_trylock_bh_state(bh)) {
				jbd_sync_bh(journal, bh);
				retry = 1;
				break;
			}
			retry = __process_buffer(journal, jh, &batch_count,
						 transaction);
			if (retry < 0 && !result)
				result = retry;
			if (!retry && (need_resched() ||
				spin_needbreak(&journal->j_list_lock))) {
				spin_unlock(&journal->j_list_lock);
				retry = 1;
				break;
			}
		}

		if (batch_count) {
			if (!retry) {
				spin_unlock(&journal->j_list_lock);
				retry = 1;
			}
			__flush_batch(journal, &batch_count);
		}

		if (retry) {
			spin_lock(&journal->j_list_lock);
			goto restart;
		}
		/*
		 * Now we have cleaned up the first transaction's checkpoint
		 * list. Let's clean up the second one
		 */
		err = __wait_cp_io(journal, transaction);
		if (!result)
			result = err;
	}
out:
	spin_unlock(&journal->j_list_lock);
	if (result < 0)
		jbd2_journal_abort(journal, result);
	else
		result = jbd2_cleanup_journal_tail(journal);

	return (result < 0) ? result : 0;
}

/*
 * Check the list of checkpoint transactions for the journal to see if
 * we have already got rid of any since the last update of the log tail
 * in the journal superblock.  If so, we can instantly roll the
 * superblock forward to remove those transactions from the log.
 *
 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 *
 * Called with the journal lock held.
 *
 * This is the only part of the journaling code which really needs to be
 * aware of transaction aborts.  Checkpointing involves writing to the
 * main filesystem area rather than to the journal, so it can proceed
 * even in abort state, but we must not update the super block if
 * checkpointing may have failed.  Otherwise, we would lose some metadata
 * buffers which should be written-back to the filesystem.
 */

int jbd2_cleanup_journal_tail(journal_t *journal)
{
	transaction_t * transaction;
	tid_t		first_tid;
	unsigned long	blocknr, freed;

	if (is_journal_aborted(journal))
		return 1;

	/* OK, work out the oldest transaction remaining in the log, and
	 * the log block it starts at.
	 *
	 * If the log is now empty, we need to work out which is the
	 * next transaction ID we will write, and where it will
	 * start. */

	write_lock(&journal->j_state_lock);
	spin_lock(&journal->j_list_lock);
	transaction = journal->j_checkpoint_transactions;
	if (transaction) {
		first_tid = transaction->t_tid;
		blocknr = transaction->t_log_start;
	} else if ((transaction = journal->j_committing_transaction) != NULL) {
		first_tid = transaction->t_tid;
		blocknr = transaction->t_log_start;
	} else if ((transaction = journal->j_running_transaction) != NULL) {
		first_tid = transaction->t_tid;
		blocknr = journal->j_head;
	} else {
		first_tid = journal->j_transaction_sequence;
		blocknr = journal->j_head;
	}
	spin_unlock(&journal->j_list_lock);
	J_ASSERT(blocknr != 0);

	/* If the oldest pinned transaction is at the tail of the log
           already then there's not much we can do right now. */
	if (journal->j_tail_sequence == first_tid) {
		write_unlock(&journal->j_state_lock);
		return 1;
	}

	/* OK, update the superblock to recover the freed space.
	 * Physical blocks come first: have we wrapped beyond the end of
	 * the log?  */
	freed = blocknr - journal->j_tail;
	if (blocknr < journal->j_tail)
		freed = freed + journal->j_last - journal->j_first;

	trace_jbd2_cleanup_journal_tail(journal, first_tid, blocknr, freed);
	jbd_debug(1,
		  "Cleaning journal tail from %d to %d (offset %lu), "
		  "freeing %lu\n",
		  journal->j_tail_sequence, first_tid, blocknr, freed);

	journal->j_free += freed;
	journal->j_tail_sequence = first_tid;
	journal->j_tail = blocknr;
	write_unlock(&journal->j_state_lock);

	/*
	 * If there is an external journal, we need to make sure that
	 * any data blocks that were recently written out --- perhaps
	 * by jbd2_log_do_checkpoint() --- are flushed out before we
	 * drop the transactions from the external journal.  It's
	 * unlikely this will be necessary, especially with a
	 * appropriately sized journal, but we need this to guarantee
	 * correctness.  Fortunately jbd2_cleanup_journal_tail()
	 * doesn't get called all that often.
	 */
	if ((journal->j_fs_dev != journal->j_dev) &&
	    (journal->j_flags & JBD2_BARRIER))
		blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL,
			BLKDEV_IFL_WAIT);
	if (!(journal->j_flags & JBD2_ABORT))
		jbd2_journal_update_superblock(journal, 1);
	return 0;
}


/* Checkpoint list management */

/*
 * journal_clean_one_cp_list
 *
 * Find all the written-back checkpoint buffers in the given list and release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of bufers reaped (for debug)
 */

static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
{
	struct journal_head *last_jh;
	struct journal_head *next_jh = jh;
	int ret, freed = 0;

	*released = 0;
	if (!jh)
		return 0;

	last_jh = jh->b_cpprev;
	do {
		jh = next_jh;
		next_jh = jh->b_cpnext;
		/* Use trylock because of the ranking */
		if (jbd_trylock_bh_state(jh2bh(jh))) {
			ret = __try_to_free_cp_buf(jh);
			if (ret) {
				freed++;
				if (ret == 2) {
					*released = 1;
					return freed;
				}
			}
		}
		/*
		 * This function only frees up some memory
		 * if possible so we dont have an obligation
		 * to finish processing. Bail out if preemption
		 * requested:
		 */
		if (need_resched())
			return freed;
	} while (jh != last_jh);

	return freed;
}

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of buffers reaped (for debug)
 */

int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
{
	transaction_t *transaction, *last_transaction, *next_transaction;
	int ret = 0;
	int released;

	transaction = journal->j_checkpoint_transactions;
	if (!transaction)
		goto out;

	last_transaction = transaction->t_cpprev;
	next_transaction = transaction;
	do {
		transaction = next_transaction;
		next_transaction = transaction->t_cpnext;
		ret += journal_clean_one_cp_list(transaction->
				t_checkpoint_list, &released);
		/*
		 * This function only frees up some memory if possible so we
		 * dont have an obligation to finish processing. Bail out if
		 * preemption requested:
		 */
		if (need_resched())
			goto out;
		if (released)
			continue;
		/*
		 * It is essential that we are as careful as in the case of
		 * t_checkpoint_list with removing the buffer from the list as
		 * we can possibly see not yet submitted buffers on io_list
		 */
		ret += journal_clean_one_cp_list(transaction->
				t_checkpoint_io_list, &released);
		if (need_resched())
			goto out;
	} while (transaction != last_transaction);
out:
	return ret;
}

/*
 * journal_remove_checkpoint: called after a buffer has been committed
 * to disk (either by being write-back flushed to disk, or being
 * committed to the log).
 *
 * We cannot safely clean a transaction out of the log until all of the
 * buffer updates committed in that transaction have safely been stored
 * elsewhere on disk.  To achieve this, all of the buffers in a
 * transaction need to be maintained on the transaction's checkpoint
 * lists until they have been rewritten, at which point this function is
 * called to remove the buffer from the existing transaction's
 * checkpoint lists.
 *
 * The function returns 1 if it frees the transaction, 0 otherwise.
 *
 * This function is called with the journal locked.
 * This function is called with j_list_lock held.
 * This function is called with jbd_lock_bh_state(jh2bh(jh))
 */

int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
{
	struct transaction_chp_stats_s *stats;
	transaction_t *transaction;
	journal_t *journal;
	int ret = 0;

	JBUFFER_TRACE(jh, "entry");

	if ((transaction = jh->b_cp_transaction) == NULL) {
		JBUFFER_TRACE(jh, "not on transaction");
		goto out;
	}
	journal = transaction->t_journal;

	__buffer_unlink(jh);
	jh->b_cp_transaction = NULL;

	if (transaction->t_checkpoint_list != NULL ||
	    transaction->t_checkpoint_io_list != NULL)
		goto out;
	JBUFFER_TRACE(jh, "transaction has no more buffers");

	/*
	 * There is one special case to worry about: if we have just pulled the
	 * buffer off a running or committing transaction's checkpoing list,
	 * then even if the checkpoint list is empty, the transaction obviously
	 * cannot be dropped!
	 *
	 * The locking here around t_state is a bit sleazy.
	 * See the comment at the end of jbd2_journal_commit_transaction().
	 */
	if (transaction->t_state != T_FINISHED) {
		JBUFFER_TRACE(jh, "belongs to running/committing transaction");
		goto out;
	}

	/* OK, that was the last buffer for the transaction: we can now
	   safely remove this transaction from the log */
	stats = &transaction->t_chp_stats;
	if (stats->cs_chp_time)
		stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
						    jiffies);
	trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
				    transaction->t_tid, stats);

	__jbd2_journal_drop_transaction(journal, transaction);
	kfree(transaction);

	/* Just in case anybody was waiting for more transactions to be
           checkpointed... */
	wake_up(&journal->j_wait_logspace);
	ret = 1;
out:
	JBUFFER_TRACE(jh, "exit");
	return ret;
}

/*
 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 * list so that we know when it is safe to clean the transaction out of
 * the log.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */
void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
			       transaction_t *transaction)
{
	JBUFFER_TRACE(jh, "entry");
	J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
	J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

	jh->b_cp_transaction = transaction;

	if (!transaction->t_checkpoint_list) {
		jh->b_cpnext = jh->b_cpprev = jh;
	} else {
		jh->b_cpnext = transaction->t_checkpoint_list;
		jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
		jh->b_cpprev->b_cpnext = jh;
		jh->b_cpnext->b_cpprev = jh;
	}
	transaction->t_checkpoint_list = jh;
}

/*
 * We've finished with this transaction structure: adios...
 *
 * The transaction must have no links except for the checkpoint by this
 * point.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */

void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
	assert_spin_locked(&journal->j_list_lock);
	if (transaction->t_cpnext) {
		transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
		transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
		if (journal->j_checkpoint_transactions == transaction)
			journal->j_checkpoint_transactions =
				transaction->t_cpnext;
		if (journal->j_checkpoint_transactions == transaction)
			journal->j_checkpoint_transactions = NULL;
	}

	J_ASSERT(transaction->t_state == T_FINISHED);
	J_ASSERT(transaction->t_buffers == NULL);
	J_ASSERT(transaction->t_forget == NULL);
	J_ASSERT(transaction->t_iobuf_list == NULL);
	J_ASSERT(transaction->t_shadow_list == NULL);
	J_ASSERT(transaction->t_log_list == NULL);
	J_ASSERT(transaction->t_checkpoint_list == NULL);
	J_ASSERT(transaction->t_checkpoint_io_list == NULL);
	J_ASSERT(atomic_read(&transaction->t_updates) == 0);
	J_ASSERT(journal->j_committing_transaction != transaction);
	J_ASSERT(journal->j_running_transaction != transaction);

	jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
}