fs/jbd2/checkpoint.c

   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], REQ_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 }