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Linux/fs/jbd2/checkpoint.c

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  1 /*
  2  * linux/fs/jbd2/checkpoint.c
  3  *
  4  * Written by Stephen C. Tweedie <sct@redhat.com>, 1999
  5  *
  6  * Copyright 1999 Red Hat Software --- All Rights Reserved
  7  *
  8  * This file is part of the Linux kernel and is made available under
  9  * the terms of the GNU General Public License, version 2, or at your
 10  * option, any later version, incorporated herein by reference.
 11  *
 12  * Checkpoint routines for the generic filesystem journaling code.
 13  * Part of the ext2fs journaling system.
 14  *
 15  * Checkpointing is the process of ensuring that a section of the log is
 16  * committed fully to disk, so that that portion of the log can be
 17  * reused.
 18  */
 19 
 20 #include <linux/time.h>
 21 #include <linux/fs.h>
 22 #include <linux/jbd2.h>
 23 #include <linux/errno.h>
 24 #include <linux/slab.h>
 25 #include <linux/blkdev.h>
 26 #include <trace/events/jbd2.h>
 27 
 28 /*
 29  * Unlink a buffer from a transaction checkpoint list.
 30  *
 31  * Called with j_list_lock held.
 32  */
 33 static inline void __buffer_unlink_first(struct journal_head *jh)
 34 {
 35         transaction_t *transaction = jh->b_cp_transaction;
 36 
 37         jh->b_cpnext->b_cpprev = jh->b_cpprev;
 38         jh->b_cpprev->b_cpnext = jh->b_cpnext;
 39         if (transaction->t_checkpoint_list == jh) {
 40                 transaction->t_checkpoint_list = jh->b_cpnext;
 41                 if (transaction->t_checkpoint_list == jh)
 42                         transaction->t_checkpoint_list = NULL;
 43         }
 44 }
 45 
 46 /*
 47  * Unlink a buffer from a transaction checkpoint(io) list.
 48  *
 49  * Called with j_list_lock held.
 50  */
 51 static inline void __buffer_unlink(struct journal_head *jh)
 52 {
 53         transaction_t *transaction = jh->b_cp_transaction;
 54 
 55         __buffer_unlink_first(jh);
 56         if (transaction->t_checkpoint_io_list == jh) {
 57                 transaction->t_checkpoint_io_list = jh->b_cpnext;
 58                 if (transaction->t_checkpoint_io_list == jh)
 59                         transaction->t_checkpoint_io_list = NULL;
 60         }
 61 }
 62 
 63 /*
 64  * Move a buffer from the checkpoint list to the checkpoint io list
 65  *
 66  * Called with j_list_lock held
 67  */
 68 static inline void __buffer_relink_io(struct journal_head *jh)
 69 {
 70         transaction_t *transaction = jh->b_cp_transaction;
 71 
 72         __buffer_unlink_first(jh);
 73 
 74         if (!transaction->t_checkpoint_io_list) {
 75                 jh->b_cpnext = jh->b_cpprev = jh;
 76         } else {
 77                 jh->b_cpnext = transaction->t_checkpoint_io_list;
 78                 jh->b_cpprev = transaction->t_checkpoint_io_list->b_cpprev;
 79                 jh->b_cpprev->b_cpnext = jh;
 80                 jh->b_cpnext->b_cpprev = jh;
 81         }
 82         transaction->t_checkpoint_io_list = jh;
 83 }
 84 
 85 /*
 86  * Try to release a checkpointed buffer from its transaction.
 87  * Returns 1 if we released it and 2 if we also released the
 88  * whole transaction.
 89  *
 90  * Requires j_list_lock
 91  */
 92 static int __try_to_free_cp_buf(struct journal_head *jh)
 93 {
 94         int ret = 0;
 95         struct buffer_head *bh = jh2bh(jh);
 96 
 97         if (jh->b_transaction == NULL && !buffer_locked(bh) &&
 98             !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
 99                 JBUFFER_TRACE(jh, "remove from checkpoint list");
100                 ret = __jbd2_journal_remove_checkpoint(jh) + 1;
101         }
102         return ret;
103 }
104 
105 /*
106  * __jbd2_log_wait_for_space: wait until there is space in the journal.
107  *
108  * Called under j-state_lock *only*.  It will be unlocked if we have to wait
109  * for a checkpoint to free up some space in the log.
110  */
111 void __jbd2_log_wait_for_space(journal_t *journal)
112 {
113         int nblocks, space_left;
114         /* assert_spin_locked(&journal->j_state_lock); */
115 
116         nblocks = jbd2_space_needed(journal);
117         while (jbd2_log_space_left(journal) < nblocks) {
118                 write_unlock(&journal->j_state_lock);
119                 mutex_lock(&journal->j_checkpoint_mutex);
120 
121                 /*
122                  * Test again, another process may have checkpointed while we
123                  * were waiting for the checkpoint lock. If there are no
124                  * transactions ready to be checkpointed, try to recover
125                  * journal space by calling cleanup_journal_tail(), and if
126                  * that doesn't work, by waiting for the currently committing
127                  * transaction to complete.  If there is absolutely no way
128                  * to make progress, this is either a BUG or corrupted
129                  * filesystem, so abort the journal and leave a stack
130                  * trace for forensic evidence.
131                  */
132                 write_lock(&journal->j_state_lock);
133                 if (journal->j_flags & JBD2_ABORT) {
134                         mutex_unlock(&journal->j_checkpoint_mutex);
135                         return;
136                 }
137                 spin_lock(&journal->j_list_lock);
138                 nblocks = jbd2_space_needed(journal);
139                 space_left = jbd2_log_space_left(journal);
140                 if (space_left < nblocks) {
141                         int chkpt = journal->j_checkpoint_transactions != NULL;
142                         tid_t tid = 0;
143 
144                         if (journal->j_committing_transaction)
145                                 tid = journal->j_committing_transaction->t_tid;
146                         spin_unlock(&journal->j_list_lock);
147                         write_unlock(&journal->j_state_lock);
148                         if (chkpt) {
149                                 jbd2_log_do_checkpoint(journal);
150                         } else if (jbd2_cleanup_journal_tail(journal) == 0) {
151                                 /* We were able to recover space; yay! */
152                                 ;
153                         } else if (tid) {
154                                 /*
155                                  * jbd2_journal_commit_transaction() may want
156                                  * to take the checkpoint_mutex if JBD2_FLUSHED
157                                  * is set.  So we need to temporarily drop it.
158                                  */
159                                 mutex_unlock(&journal->j_checkpoint_mutex);
160                                 jbd2_log_wait_commit(journal, tid);
161                                 write_lock(&journal->j_state_lock);
162                                 continue;
163                         } else {
164                                 printk(KERN_ERR "%s: needed %d blocks and "
165                                        "only had %d space available\n",
166                                        __func__, nblocks, space_left);
167                                 printk(KERN_ERR "%s: no way to get more "
168                                        "journal space in %s\n", __func__,
169                                        journal->j_devname);
170                                 WARN_ON(1);
171                                 jbd2_journal_abort(journal, 0);
172                         }
173                         write_lock(&journal->j_state_lock);
174                 } else {
175                         spin_unlock(&journal->j_list_lock);
176                 }
177                 mutex_unlock(&journal->j_checkpoint_mutex);
178         }
179 }
180 
181 static void
182 __flush_batch(journal_t *journal, int *batch_count)
183 {
184         int i;
185         struct blk_plug plug;
186 
187         blk_start_plug(&plug);
188         for (i = 0; i < *batch_count; i++)
189                 write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE_SYNC);
190         blk_finish_plug(&plug);
191 
192         for (i = 0; i < *batch_count; i++) {
193                 struct buffer_head *bh = journal->j_chkpt_bhs[i];
194                 BUFFER_TRACE(bh, "brelse");
195                 __brelse(bh);
196         }
197         *batch_count = 0;
198 }
199 
200 /*
201  * Perform an actual checkpoint. We take the first transaction on the
202  * list of transactions to be checkpointed and send all its buffers
203  * to disk. We submit larger chunks of data at once.
204  *
205  * The journal should be locked before calling this function.
206  * Called with j_checkpoint_mutex held.
207  */
208 int jbd2_log_do_checkpoint(journal_t *journal)
209 {
210         struct journal_head     *jh;
211         struct buffer_head      *bh;
212         transaction_t           *transaction;
213         tid_t                   this_tid;
214         int                     result, batch_count = 0;
215 
216         jbd_debug(1, "Start checkpoint\n");
217 
218         /*
219          * First thing: if there are any transactions in the log which
220          * don't need checkpointing, just eliminate them from the
221          * journal straight away.
222          */
223         result = jbd2_cleanup_journal_tail(journal);
224         trace_jbd2_checkpoint(journal, result);
225         jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
226         if (result <= 0)
227                 return result;
228 
229         /*
230          * OK, we need to start writing disk blocks.  Take one transaction
231          * and write it.
232          */
233         result = 0;
234         spin_lock(&journal->j_list_lock);
235         if (!journal->j_checkpoint_transactions)
236                 goto out;
237         transaction = journal->j_checkpoint_transactions;
238         if (transaction->t_chp_stats.cs_chp_time == 0)
239                 transaction->t_chp_stats.cs_chp_time = jiffies;
240         this_tid = transaction->t_tid;
241 restart:
242         /*
243          * If someone cleaned up this transaction while we slept, we're
244          * done (maybe it's a new transaction, but it fell at the same
245          * address).
246          */
247         if (journal->j_checkpoint_transactions != transaction ||
248             transaction->t_tid != this_tid)
249                 goto out;
250 
251         /* checkpoint all of the transaction's buffers */
252         while (transaction->t_checkpoint_list) {
253                 jh = transaction->t_checkpoint_list;
254                 bh = jh2bh(jh);
255 
256                 if (buffer_locked(bh)) {
257                         spin_unlock(&journal->j_list_lock);
258                         get_bh(bh);
259                         wait_on_buffer(bh);
260                         /* the journal_head may have gone by now */
261                         BUFFER_TRACE(bh, "brelse");
262                         __brelse(bh);
263                         goto retry;
264                 }
265                 if (jh->b_transaction != NULL) {
266                         transaction_t *t = jh->b_transaction;
267                         tid_t tid = t->t_tid;
268 
269                         transaction->t_chp_stats.cs_forced_to_close++;
270                         spin_unlock(&journal->j_list_lock);
271                         if (unlikely(journal->j_flags & JBD2_UNMOUNT))
272                                 /*
273                                  * The journal thread is dead; so
274                                  * starting and waiting for a commit
275                                  * to finish will cause us to wait for
276                                  * a _very_ long time.
277                                  */
278                                 printk(KERN_ERR
279                 "JBD2: %s: Waiting for Godot: block %llu\n",
280                 journal->j_devname, (unsigned long long) bh->b_blocknr);
281 
282                         jbd2_log_start_commit(journal, tid);
283                         jbd2_log_wait_commit(journal, tid);
284                         goto retry;
285                 }
286                 if (!buffer_dirty(bh)) {
287                         if (unlikely(buffer_write_io_error(bh)) && !result)
288                                 result = -EIO;
289                         BUFFER_TRACE(bh, "remove from checkpoint");
290                         if (__jbd2_journal_remove_checkpoint(jh))
291                                 /* The transaction was released; we're done */
292                                 goto out;
293                         continue;
294                 }
295                 /*
296                  * Important: we are about to write the buffer, and
297                  * possibly block, while still holding the journal
298                  * lock.  We cannot afford to let the transaction
299                  * logic start messing around with this buffer before
300                  * we write it to disk, as that would break
301                  * recoverability.
302                  */
303                 BUFFER_TRACE(bh, "queue");
304                 get_bh(bh);
305                 J_ASSERT_BH(bh, !buffer_jwrite(bh));
306                 journal->j_chkpt_bhs[batch_count++] = bh;
307                 __buffer_relink_io(jh);
308                 transaction->t_chp_stats.cs_written++;
309                 if ((batch_count == JBD2_NR_BATCH) ||
310                     need_resched() ||
311                     spin_needbreak(&journal->j_list_lock))
312                         goto unlock_and_flush;
313         }
314 
315         if (batch_count) {
316                 unlock_and_flush:
317                         spin_unlock(&journal->j_list_lock);
318                 retry:
319                         if (batch_count)
320                                 __flush_batch(journal, &batch_count);
321                         spin_lock(&journal->j_list_lock);
322                         goto restart;
323         }
324 
325         /*
326          * Now we issued all of the transaction's buffers, let's deal
327          * with the buffers that are out for I/O.
328          */
329 restart2:
330         /* Did somebody clean up the transaction in the meanwhile? */
331         if (journal->j_checkpoint_transactions != transaction ||
332             transaction->t_tid != this_tid)
333                 goto out;
334 
335         while (transaction->t_checkpoint_io_list) {
336                 jh = transaction->t_checkpoint_io_list;
337                 bh = jh2bh(jh);
338                 if (buffer_locked(bh)) {
339                         spin_unlock(&journal->j_list_lock);
340                         get_bh(bh);
341                         wait_on_buffer(bh);
342                         /* the journal_head may have gone by now */
343                         BUFFER_TRACE(bh, "brelse");
344                         __brelse(bh);
345                         spin_lock(&journal->j_list_lock);
346                         goto restart2;
347                 }
348                 if (unlikely(buffer_write_io_error(bh)) && !result)
349                         result = -EIO;
350 
351                 /*
352                  * Now in whatever state the buffer currently is, we
353                  * know that it has been written out and so we can
354                  * drop it from the list
355                  */
356                 if (__jbd2_journal_remove_checkpoint(jh))
357                         break;
358         }
359 out:
360         spin_unlock(&journal->j_list_lock);
361         if (result < 0)
362                 jbd2_journal_abort(journal, result);
363         else
364                 result = jbd2_cleanup_journal_tail(journal);
365 
366         return (result < 0) ? result : 0;
367 }
368 
369 /*
370  * Check the list of checkpoint transactions for the journal to see if
371  * we have already got rid of any since the last update of the log tail
372  * in the journal superblock.  If so, we can instantly roll the
373  * superblock forward to remove those transactions from the log.
374  *
375  * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
376  *
377  * Called with the journal lock held.
378  *
379  * This is the only part of the journaling code which really needs to be
380  * aware of transaction aborts.  Checkpointing involves writing to the
381  * main filesystem area rather than to the journal, so it can proceed
382  * even in abort state, but we must not update the super block if
383  * checkpointing may have failed.  Otherwise, we would lose some metadata
384  * buffers which should be written-back to the filesystem.
385  */
386 
387 int jbd2_cleanup_journal_tail(journal_t *journal)
388 {
389         tid_t           first_tid;
390         unsigned long   blocknr;
391 
392         if (is_journal_aborted(journal))
393                 return -EIO;
394 
395         if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
396                 return 1;
397         J_ASSERT(blocknr != 0);
398 
399         /*
400          * We need to make sure that any blocks that were recently written out
401          * --- perhaps by jbd2_log_do_checkpoint() --- are flushed out before
402          * we drop the transactions from the journal. It's unlikely this will
403          * be necessary, especially with an appropriately sized journal, but we
404          * need this to guarantee correctness.  Fortunately
405          * jbd2_cleanup_journal_tail() doesn't get called all that often.
406          */
407         if (journal->j_flags & JBD2_BARRIER)
408                 blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL);
409 
410         return __jbd2_update_log_tail(journal, first_tid, blocknr);
411 }
412 
413 
414 /* Checkpoint list management */
415 
416 /*
417  * journal_clean_one_cp_list
418  *
419  * Find all the written-back checkpoint buffers in the given list and
420  * release them. If 'destroy' is set, clean all buffers unconditionally.
421  *
422  * Called with j_list_lock held.
423  * Returns 1 if we freed the transaction, 0 otherwise.
424  */
425 static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
426 {
427         struct journal_head *last_jh;
428         struct journal_head *next_jh = jh;
429         int ret;
430 
431         if (!jh)
432                 return 0;
433 
434         last_jh = jh->b_cpprev;
435         do {
436                 jh = next_jh;
437                 next_jh = jh->b_cpnext;
438                 if (!destroy)
439                         ret = __try_to_free_cp_buf(jh);
440                 else
441                         ret = __jbd2_journal_remove_checkpoint(jh) + 1;
442                 if (!ret)
443                         return 0;
444                 if (ret == 2)
445                         return 1;
446                 /*
447                  * This function only frees up some memory
448                  * if possible so we dont have an obligation
449                  * to finish processing. Bail out if preemption
450                  * requested:
451                  */
452                 if (need_resched())
453                         return 0;
454         } while (jh != last_jh);
455 
456         return 0;
457 }
458 
459 /*
460  * journal_clean_checkpoint_list
461  *
462  * Find all the written-back checkpoint buffers in the journal and release them.
463  * If 'destroy' is set, release all buffers unconditionally.
464  *
465  * Called with j_list_lock held.
466  */
467 void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy)
468 {
469         transaction_t *transaction, *last_transaction, *next_transaction;
470         int ret;
471 
472         transaction = journal->j_checkpoint_transactions;
473         if (!transaction)
474                 return;
475 
476         last_transaction = transaction->t_cpprev;
477         next_transaction = transaction;
478         do {
479                 transaction = next_transaction;
480                 next_transaction = transaction->t_cpnext;
481                 ret = journal_clean_one_cp_list(transaction->t_checkpoint_list,
482                                                 destroy);
483                 /*
484                  * This function only frees up some memory if possible so we
485                  * dont have an obligation to finish processing. Bail out if
486                  * preemption requested:
487                  */
488                 if (need_resched())
489                         return;
490                 if (ret)
491                         continue;
492                 /*
493                  * It is essential that we are as careful as in the case of
494                  * t_checkpoint_list with removing the buffer from the list as
495                  * we can possibly see not yet submitted buffers on io_list
496                  */
497                 ret = journal_clean_one_cp_list(transaction->
498                                 t_checkpoint_io_list, destroy);
499                 if (need_resched())
500                         return;
501                 /*
502                  * Stop scanning if we couldn't free the transaction. This
503                  * avoids pointless scanning of transactions which still
504                  * weren't checkpointed.
505                  */
506                 if (!ret)
507                         return;
508         } while (transaction != last_transaction);
509 }
510 
511 /*
512  * Remove buffers from all checkpoint lists as journal is aborted and we just
513  * need to free memory
514  */
515 void jbd2_journal_destroy_checkpoint(journal_t *journal)
516 {
517         /*
518          * We loop because __jbd2_journal_clean_checkpoint_list() may abort
519          * early due to a need of rescheduling.
520          */
521         while (1) {
522                 spin_lock(&journal->j_list_lock);
523                 if (!journal->j_checkpoint_transactions) {
524                         spin_unlock(&journal->j_list_lock);
525                         break;
526                 }
527                 __jbd2_journal_clean_checkpoint_list(journal, true);
528                 spin_unlock(&journal->j_list_lock);
529                 cond_resched();
530         }
531 }
532 
533 /*
534  * journal_remove_checkpoint: called after a buffer has been committed
535  * to disk (either by being write-back flushed to disk, or being
536  * committed to the log).
537  *
538  * We cannot safely clean a transaction out of the log until all of the
539  * buffer updates committed in that transaction have safely been stored
540  * elsewhere on disk.  To achieve this, all of the buffers in a
541  * transaction need to be maintained on the transaction's checkpoint
542  * lists until they have been rewritten, at which point this function is
543  * called to remove the buffer from the existing transaction's
544  * checkpoint lists.
545  *
546  * The function returns 1 if it frees the transaction, 0 otherwise.
547  * The function can free jh and bh.
548  *
549  * This function is called with j_list_lock held.
550  */
551 int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
552 {
553         struct transaction_chp_stats_s *stats;
554         transaction_t *transaction;
555         journal_t *journal;
556         int ret = 0;
557 
558         JBUFFER_TRACE(jh, "entry");
559 
560         if ((transaction = jh->b_cp_transaction) == NULL) {
561                 JBUFFER_TRACE(jh, "not on transaction");
562                 goto out;
563         }
564         journal = transaction->t_journal;
565 
566         JBUFFER_TRACE(jh, "removing from transaction");
567         __buffer_unlink(jh);
568         jh->b_cp_transaction = NULL;
569         jbd2_journal_put_journal_head(jh);
570 
571         if (transaction->t_checkpoint_list != NULL ||
572             transaction->t_checkpoint_io_list != NULL)
573                 goto out;
574 
575         /*
576          * There is one special case to worry about: if we have just pulled the
577          * buffer off a running or committing transaction's checkpoing list,
578          * then even if the checkpoint list is empty, the transaction obviously
579          * cannot be dropped!
580          *
581          * The locking here around t_state is a bit sleazy.
582          * See the comment at the end of jbd2_journal_commit_transaction().
583          */
584         if (transaction->t_state != T_FINISHED)
585                 goto out;
586 
587         /* OK, that was the last buffer for the transaction: we can now
588            safely remove this transaction from the log */
589         stats = &transaction->t_chp_stats;
590         if (stats->cs_chp_time)
591                 stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
592                                                     jiffies);
593         trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
594                                     transaction->t_tid, stats);
595 
596         __jbd2_journal_drop_transaction(journal, transaction);
597         jbd2_journal_free_transaction(transaction);
598         ret = 1;
599 out:
600         return ret;
601 }
602 
603 /*
604  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
605  * list so that we know when it is safe to clean the transaction out of
606  * the log.
607  *
608  * Called with the journal locked.
609  * Called with j_list_lock held.
610  */
611 void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
612                                transaction_t *transaction)
613 {
614         JBUFFER_TRACE(jh, "entry");
615         J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
616         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
617 
618         /* Get reference for checkpointing transaction */
619         jbd2_journal_grab_journal_head(jh2bh(jh));
620         jh->b_cp_transaction = transaction;
621 
622         if (!transaction->t_checkpoint_list) {
623                 jh->b_cpnext = jh->b_cpprev = jh;
624         } else {
625                 jh->b_cpnext = transaction->t_checkpoint_list;
626                 jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
627                 jh->b_cpprev->b_cpnext = jh;
628                 jh->b_cpnext->b_cpprev = jh;
629         }
630         transaction->t_checkpoint_list = jh;
631 }
632 
633 /*
634  * We've finished with this transaction structure: adios...
635  *
636  * The transaction must have no links except for the checkpoint by this
637  * point.
638  *
639  * Called with the journal locked.
640  * Called with j_list_lock held.
641  */
642 
643 void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
644 {
645         assert_spin_locked(&journal->j_list_lock);
646         if (transaction->t_cpnext) {
647                 transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
648                 transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
649                 if (journal->j_checkpoint_transactions == transaction)
650                         journal->j_checkpoint_transactions =
651                                 transaction->t_cpnext;
652                 if (journal->j_checkpoint_transactions == transaction)
653                         journal->j_checkpoint_transactions = NULL;
654         }
655 
656         J_ASSERT(transaction->t_state == T_FINISHED);
657         J_ASSERT(transaction->t_buffers == NULL);
658         J_ASSERT(transaction->t_forget == NULL);
659         J_ASSERT(transaction->t_shadow_list == NULL);
660         J_ASSERT(transaction->t_checkpoint_list == NULL);
661         J_ASSERT(transaction->t_checkpoint_io_list == NULL);
662         J_ASSERT(atomic_read(&transaction->t_updates) == 0);
663         J_ASSERT(journal->j_committing_transaction != transaction);
664         J_ASSERT(journal->j_running_transaction != transaction);
665 
666         trace_jbd2_drop_transaction(journal, transaction);
667 
668         jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
669 }
670 

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