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   1 /*
   2  * linux/fs/jbd/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/jbd.h>
  23 #include <linux/errno.h>
  24 #include <linux/slab.h>
  25
  26 /*
  27  * Unlink a buffer from a transaction checkpoint list.
  28  *
  29  * Called with j_list_lock held.
  30  */
  31 static inline void __buffer_unlink_first(struct journal_head *jh)
  32 {
  33         transaction_t *transaction = jh->b_cp_transaction;
  34
  35         jh->b_cpnext->b_cpprev = jh->b_cpprev;
  36         jh->b_cpprev->b_cpnext = jh->b_cpnext;
  37         if (transaction->t_checkpoint_list == jh) {
  38                 transaction->t_checkpoint_list = jh->b_cpnext;
  39                 if (transaction->t_checkpoint_list == jh)
  40                         transaction->t_checkpoint_list = NULL;
  41         }
  42 }
  43
  44 /*
  45  * Unlink a buffer from a transaction checkpoint(io) list.
  46  *
  47  * Called with j_list_lock held.
  48  */
  49 static inline void __buffer_unlink(struct journal_head *jh)
  50 {
  51         transaction_t *transaction = jh->b_cp_transaction;
  52
  53         __buffer_unlink_first(jh);
  54         if (transaction->t_checkpoint_io_list == jh) {
  55                 transaction->t_checkpoint_io_list = jh->b_cpnext;
  56                 if (transaction->t_checkpoint_io_list == jh)
  57                         transaction->t_checkpoint_io_list = NULL;
  58         }
  59 }
  60
  61 /*
  62  * Move a buffer from the checkpoint list to the checkpoint io list
  63  *
  64  * Called with j_list_lock held
  65  */
  66 static inline void __buffer_relink_io(struct journal_head *jh)
  67 {
  68         transaction_t *transaction = jh->b_cp_transaction;
  69
  70         __buffer_unlink_first(jh);
  71
  72         if (!transaction->t_checkpoint_io_list) {
  73                 jh->b_cpnext = jh->b_cpprev = jh;
  74         } else {
  75                 jh->b_cpnext = transaction->t_checkpoint_io_list;
  76                 jh->b_cpprev = transaction->t_checkpoint_io_list->b_cpprev;
  77                 jh->b_cpprev->b_cpnext = jh;
  78                 jh->b_cpnext->b_cpprev = jh;
  79         }
  80         transaction->t_checkpoint_io_list = jh;
  81 }
  82
  83 /*
  84  * Try to release a checkpointed buffer from its transaction.
  85  * Returns 1 if we released it and 2 if we also released the
  86  * whole transaction.
  87  *
  88  * Requires j_list_lock
  89  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
  90  */
  91 static int __try_to_free_cp_buf(struct journal_head *jh)
  92 {
  93         int ret = 0;
  94         struct buffer_head *bh = jh2bh(jh);
  95
  96         if (jh->b_jlist == BJ_None && !buffer_locked(bh) && !buffer_dirty(bh)) {
  97                 JBUFFER_TRACE(jh, "remove from checkpoint list");
  98                 ret = __journal_remove_checkpoint(jh) + 1;
  99                 jbd_unlock_bh_state(bh);
 100                 journal_remove_journal_head(bh);
 101                 BUFFER_TRACE(bh, "release");
 102                 __brelse(bh);
 103         } else {
 104                 jbd_unlock_bh_state(bh);
 105         }
 106         return ret;
 107 }
 108
 109 /*
 110  * __log_wait_for_space: wait until there is space in the journal.
 111  *
 112  * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 113  * for a checkpoint to free up some space in the log.
 114  */
 115 void __log_wait_for_space(journal_t *journal)
 116 {
 117         int nblocks;
 118         assert_spin_locked(&journal->j_state_lock);
 119
 120         nblocks = jbd_space_needed(journal);
 121         while (__log_space_left(journal) < nblocks) {
 122                 if (journal->j_flags & JFS_ABORT)
 123                         return;
 124                 spin_unlock(&journal->j_state_lock);
 125                 mutex_lock(&journal->j_checkpoint_mutex);
 126
 127                 /*
 128                  * Test again, another process may have checkpointed while we
 129                  * were waiting for the checkpoint lock
 130                  */
 131                 spin_lock(&journal->j_state_lock);
 132                 nblocks = jbd_space_needed(journal);
 133                 if (__log_space_left(journal) < nblocks) {
 134                         spin_unlock(&journal->j_state_lock);
 135                         log_do_checkpoint(journal);
 136                         spin_lock(&journal->j_state_lock);
 137                 }
 138                 mutex_unlock(&journal->j_checkpoint_mutex);
 139         }
 140 }
 141
 142 /*
 143  * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 144  * The caller must restart a list walk.  Wait for someone else to run
 145  * jbd_unlock_bh_state().
 146  */
 147 static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
 148         __releases(journal->j_list_lock)
 149 {
 150         get_bh(bh);
 151         spin_unlock(&journal->j_list_lock);
 152         jbd_lock_bh_state(bh);
 153         jbd_unlock_bh_state(bh);
 154         put_bh(bh);
 155 }
 156
 157 /*
 158  * Clean up transaction's list of buffers submitted for io.
 159  * We wait for any pending IO to complete and remove any clean
 160  * buffers. Note that we take the buffers in the opposite ordering
 161  * from the one in which they were submitted for IO.
 162  *
 163  * Called with j_list_lock held.
 164  */
 165 static void __wait_cp_io(journal_t *journal, transaction_t *transaction)
 166 {
 167         struct journal_head *jh;
 168         struct buffer_head *bh;
 169         tid_t this_tid;
 170         int released = 0;
 171
 172         this_tid = transaction->t_tid;
 173 restart:
 174         /* Did somebody clean up the transaction in the meanwhile? */
 175         if (journal->j_checkpoint_transactions != transaction ||
 176                         transaction->t_tid != this_tid)
 177                 return;
 178         while (!released && transaction->t_checkpoint_io_list) {
 179                 jh = transaction->t_checkpoint_io_list;
 180                 bh = jh2bh(jh);
 181                 if (!jbd_trylock_bh_state(bh)) {
 182                         jbd_sync_bh(journal, bh);
 183                         spin_lock(&journal->j_list_lock);
 184                         goto restart;
 185                 }
 186                 if (buffer_locked(bh)) {
 187                         atomic_inc(&bh->b_count);
 188                         spin_unlock(&journal->j_list_lock);
 189                         jbd_unlock_bh_state(bh);
 190                         wait_on_buffer(bh);
 191                         /* the journal_head may have gone by now */
 192                         BUFFER_TRACE(bh, "brelse");
 193                         __brelse(bh);
 194                         spin_lock(&journal->j_list_lock);
 195                         goto restart;
 196                 }
 197                 /*
 198                  * Now in whatever state the buffer currently is, we know that
 199                  * it has been written out and so we can drop it from the list
 200                  */
 201                 released = __journal_remove_checkpoint(jh);
 202                 jbd_unlock_bh_state(bh);
 203                 journal_remove_journal_head(bh);
 204                 __brelse(bh);
 205         }
 206 }
 207
 208 #define NR_BATCH        64
 209
 210 static void
 211 __flush_batch(journal_t *journal, struct buffer_head **bhs, int *batch_count)
 212 {
 213         int i;
 214
 215         ll_rw_block(SWRITE, *batch_count, bhs);
 216         for (i = 0; i < *batch_count; i++) {
 217                 struct buffer_head *bh = bhs[i];
 218                 clear_buffer_jwrite(bh);
 219                 BUFFER_TRACE(bh, "brelse");
 220                 __brelse(bh);
 221         }
 222         *batch_count = 0;
 223 }
 224
 225 /*
 226  * Try to flush one buffer from the checkpoint list to disk.
 227  *
 228  * Return 1 if something happened which requires us to abort the current
 229  * scan of the checkpoint list.
 230  *
 231  * Called with j_list_lock held and drops it if 1 is returned
 232  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 233  */
 234 static int __process_buffer(journal_t *journal, struct journal_head *jh,
 235                         struct buffer_head **bhs, int *batch_count)
 236 {
 237         struct buffer_head *bh = jh2bh(jh);
 238         int ret = 0;
 239
 240         if (buffer_locked(bh)) {
 241                 atomic_inc(&bh->b_count);
 242                 spin_unlock(&journal->j_list_lock);
 243                 jbd_unlock_bh_state(bh);
 244                 wait_on_buffer(bh);
 245                 /* the journal_head may have gone by now */
 246                 BUFFER_TRACE(bh, "brelse");
 247                 __brelse(bh);
 248                 ret = 1;
 249         } else if (jh->b_transaction != NULL) {
 250                 transaction_t *t = jh->b_transaction;
 251                 tid_t tid = t->t_tid;
 252
 253                 spin_unlock(&journal->j_list_lock);
 254                 jbd_unlock_bh_state(bh);
 255                 log_start_commit(journal, tid);
 256                 log_wait_commit(journal, tid);
 257                 ret = 1;
 258         } else if (!buffer_dirty(bh)) {
 259                 J_ASSERT_JH(jh, !buffer_jbddirty(bh));
 260                 BUFFER_TRACE(bh, "remove from checkpoint");
 261                 __journal_remove_checkpoint(jh);
 262                 spin_unlock(&journal->j_list_lock);
 263                 jbd_unlock_bh_state(bh);
 264                 journal_remove_journal_head(bh);
 265                 __brelse(bh);
 266                 ret = 1;
 267         } else {
 268                 /*
 269                  * Important: we are about to write the buffer, and
 270                  * possibly block, while still holding the journal lock.
 271                  * We cannot afford to let the transaction logic start
 272                  * messing around with this buffer before we write it to
 273                  * disk, as that would break recoverability.
 274                  */
 275                 BUFFER_TRACE(bh, "queue");
 276                 get_bh(bh);
 277                 J_ASSERT_BH(bh, !buffer_jwrite(bh));
 278                 set_buffer_jwrite(bh);
 279                 bhs[*batch_count] = bh;
 280                 __buffer_relink_io(jh);
 281                 jbd_unlock_bh_state(bh);
 282                 (*batch_count)++;
 283                 if (*batch_count == NR_BATCH) {
 284                         spin_unlock(&journal->j_list_lock);
 285                         __flush_batch(journal, bhs, batch_count);
 286                         ret = 1;
 287                 }
 288         }
 289         return ret;
 290 }
 291
 292 /*
 293  * Perform an actual checkpoint. We take the first transaction on the
 294  * list of transactions to be checkpointed and send all its buffers
 295  * to disk. We submit larger chunks of data at once.
 296  *
 297  * The journal should be locked before calling this function.
 298  */
 299 int log_do_checkpoint(journal_t *journal)
 300 {
 301         transaction_t *transaction;
 302         tid_t this_tid;
 303         int result;
 304
 305         jbd_debug(1, "Start checkpoint\n");
 306
 307         /*
 308          * First thing: if there are any transactions in the log which
 309          * don't need checkpointing, just eliminate them from the
 310          * journal straight away.
 311          */
 312         result = cleanup_journal_tail(journal);
 313         jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
 314         if (result <= 0)
 315                 return result;
 316
 317         /*
 318          * OK, we need to start writing disk blocks.  Take one transaction
 319          * and write it.
 320          */
 321         spin_lock(&journal->j_list_lock);
 322         if (!journal->j_checkpoint_transactions)
 323                 goto out;
 324         transaction = journal->j_checkpoint_transactions;
 325         this_tid = transaction->t_tid;
 326 restart:
 327         /*
 328          * If someone cleaned up this transaction while we slept, we're
 329          * done (maybe it's a new transaction, but it fell at the same
 330          * address).
 331          */
 332         if (journal->j_checkpoint_transactions == transaction &&
 333                         transaction->t_tid == this_tid) {
 334                 int batch_count = 0;
 335                 struct buffer_head *bhs[NR_BATCH];
 336                 struct journal_head *jh;
 337                 int retry = 0;
 338
 339                 while (!retry && transaction->t_checkpoint_list) {
 340                         struct buffer_head *bh;
 341
 342                         jh = transaction->t_checkpoint_list;
 343                         bh = jh2bh(jh);
 344                         if (!jbd_trylock_bh_state(bh)) {
 345                                 jbd_sync_bh(journal, bh);
 346                                 retry = 1;
 347                                 break;
 348                         }
 349                         retry = __process_buffer(journal, jh, bhs,&batch_count);
 350                         if (!retry && (need_resched() ||
 351                                 spin_needbreak(&journal->j_list_lock))) {
 352                                 spin_unlock(&journal->j_list_lock);
 353                                 retry = 1;
 354                                 break;
 355                         }
 356                 }
 357
 358                 if (batch_count) {
 359                         if (!retry) {
 360                                 spin_unlock(&journal->j_list_lock);
 361                                 retry = 1;
 362                         }
 363                         __flush_batch(journal, bhs, &batch_count);
 364                 }
 365
 366                 if (retry) {
 367                         spin_lock(&journal->j_list_lock);
 368                         goto restart;
 369                 }
 370                 /*
 371                  * Now we have cleaned up the first transaction's checkpoint
 372                  * list. Let's clean up the second one
 373                  */
 374                 __wait_cp_io(journal, transaction);
 375         }
 376 out:
 377         spin_unlock(&journal->j_list_lock);
 378         result = cleanup_journal_tail(journal);
 379         if (result < 0)
 380                 return result;
 381         return 0;
 382 }
 383
 384 /*
 385  * Check the list of checkpoint transactions for the journal to see if
 386  * we have already got rid of any since the last update of the log tail
 387  * in the journal superblock.  If so, we can instantly roll the
 388  * superblock forward to remove those transactions from the log.
 389  *
 390  * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 391  *
 392  * Called with the journal lock held.
 393  *
 394  * This is the only part of the journaling code which really needs to be
 395  * aware of transaction aborts.  Checkpointing involves writing to the
 396  * main filesystem area rather than to the journal, so it can proceed
 397  * even in abort state, but we must not update the journal superblock if
 398  * we have an abort error outstanding.
 399  */
 400
 401 int cleanup_journal_tail(journal_t *journal)
 402 {
 403         transaction_t * transaction;
 404         tid_t           first_tid;
 405         unsigned long   blocknr, freed;
 406
 407         /* OK, work out the oldest transaction remaining in the log, and
 408          * the log block it starts at.
 409          *
 410          * If the log is now empty, we need to work out which is the
 411          * next transaction ID we will write, and where it will
 412          * start. */
 413
 414         spin_lock(&journal->j_state_lock);
 415         spin_lock(&journal->j_list_lock);
 416         transaction = journal->j_checkpoint_transactions;
 417         if (transaction) {
 418                 first_tid = transaction->t_tid;
 419                 blocknr = transaction->t_log_start;
 420         } else if ((transaction = journal->j_committing_transaction) != NULL) {
 421                 first_tid = transaction->t_tid;
 422                 blocknr = transaction->t_log_start;
 423         } else if ((transaction = journal->j_running_transaction) != NULL) {
 424                 first_tid = transaction->t_tid;
 425                 blocknr = journal->j_head;
 426         } else {
 427                 first_tid = journal->j_transaction_sequence;
 428                 blocknr = journal->j_head;
 429         }
 430         spin_unlock(&journal->j_list_lock);
 431         J_ASSERT(blocknr != 0);
 432
 433         /* If the oldest pinned transaction is at the tail of the log
 434            already then there's not much we can do right now. */
 435         if (journal->j_tail_sequence == first_tid) {
 436                 spin_unlock(&journal->j_state_lock);
 437                 return 1;
 438         }
 439
 440         /* OK, update the superblock to recover the freed space.
 441          * Physical blocks come first: have we wrapped beyond the end of
 442          * the log?  */
 443         freed = blocknr - journal->j_tail;
 444         if (blocknr < journal->j_tail)
 445                 freed = freed + journal->j_last - journal->j_first;
 446
 447         jbd_debug(1,
 448                   "Cleaning journal tail from %d to %d (offset %lu), "
 449                   "freeing %lu\n",
 450                   journal->j_tail_sequence, first_tid, blocknr, freed);
 451
 452         journal->j_free += freed;
 453         journal->j_tail_sequence = first_tid;
 454         journal->j_tail = blocknr;
 455         spin_unlock(&journal->j_state_lock);
 456         if (!(journal->j_flags & JFS_ABORT))
 457                 journal_update_superblock(journal, 1);
 458         return 0;
 459 }
 460
 461
 462 /* Checkpoint list management */
 463
 464 /*
 465  * journal_clean_one_cp_list
 466  *
 467  * Find all the written-back checkpoint buffers in the given list and release them.
 468  *
 469  * Called with the journal locked.
 470  * Called with j_list_lock held.
 471  * Returns number of bufers reaped (for debug)
 472  */
 473
 474 static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
 475 {
 476         struct journal_head *last_jh;
 477         struct journal_head *next_jh = jh;
 478         int ret, freed = 0;
 479
 480         *released = 0;
 481         if (!jh)
 482                 return 0;
 483
 484         last_jh = jh->b_cpprev;
 485         do {
 486                 jh = next_jh;
 487                 next_jh = jh->b_cpnext;
 488                 /* Use trylock because of the ranking */
 489                 if (jbd_trylock_bh_state(jh2bh(jh))) {
 490                         ret = __try_to_free_cp_buf(jh);
 491                         if (ret) {
 492                                 freed++;
 493                                 if (ret == 2) {
 494                                         *released = 1;
 495                                         return freed;
 496                                 }
 497                         }
 498                 }
 499                 /*
 500                  * This function only frees up some memory
 501                  * if possible so we dont have an obligation
 502                  * to finish processing. Bail out if preemption
 503                  * requested:
 504                  */
 505                 if (need_resched())
 506                         return freed;
 507         } while (jh != last_jh);
 508
 509         return freed;
 510 }
 511
 512 /*
 513  * journal_clean_checkpoint_list
 514  *
 515  * Find all the written-back checkpoint buffers in the journal and release them.
 516  *
 517  * Called with the journal locked.
 518  * Called with j_list_lock held.
 519  * Returns number of buffers reaped (for debug)
 520  */
 521
 522 int __journal_clean_checkpoint_list(journal_t *journal)
 523 {
 524         transaction_t *transaction, *last_transaction, *next_transaction;
 525         int ret = 0;
 526         int released;
 527
 528         transaction = journal->j_checkpoint_transactions;
 529         if (!transaction)
 530                 goto out;
 531
 532         last_transaction = transaction->t_cpprev;
 533         next_transaction = transaction;
 534         do {
 535                 transaction = next_transaction;
 536                 next_transaction = transaction->t_cpnext;
 537                 ret += journal_clean_one_cp_list(transaction->
 538                                 t_checkpoint_list, &released);
 539                 /*
 540                  * This function only frees up some memory if possible so we
 541                  * dont have an obligation to finish processing. Bail out if
 542                  * preemption requested:
 543                  */
 544                 if (need_resched())
 545                         goto out;
 546                 if (released)
 547                         continue;
 548                 /*
 549                  * It is essential that we are as careful as in the case of
 550                  * t_checkpoint_list with removing the buffer from the list as
 551                  * we can possibly see not yet submitted buffers on io_list
 552                  */
 553                 ret += journal_clean_one_cp_list(transaction->
 554                                 t_checkpoint_io_list, &released);
 555                 if (need_resched())
 556                         goto out;
 557         } while (transaction != last_transaction);
 558 out:
 559         return ret;
 560 }
 561
 562 /*
 563  * journal_remove_checkpoint: called after a buffer has been committed
 564  * to disk (either by being write-back flushed to disk, or being
 565  * committed to the log).
 566  *
 567  * We cannot safely clean a transaction out of the log until all of the
 568  * buffer updates committed in that transaction have safely been stored
 569  * elsewhere on disk.  To achieve this, all of the buffers in a
 570  * transaction need to be maintained on the transaction's checkpoint
 571  * lists until they have been rewritten, at which point this function is
 572  * called to remove the buffer from the existing transaction's
 573  * checkpoint lists.
 574  *
 575  * The function returns 1 if it frees the transaction, 0 otherwise.
 576  *
 577  * This function is called with the journal locked.
 578  * This function is called with j_list_lock held.
 579  * This function is called with jbd_lock_bh_state(jh2bh(jh))
 580  */
 581
 582 int __journal_remove_checkpoint(struct journal_head *jh)
 583 {
 584         transaction_t *transaction;
 585         journal_t *journal;
 586         int ret = 0;
 587
 588         JBUFFER_TRACE(jh, "entry");
 589
 590         if ((transaction = jh->b_cp_transaction) == NULL) {
 591                 JBUFFER_TRACE(jh, "not on transaction");
 592                 goto out;
 593         }
 594         journal = transaction->t_journal;
 595
 596         __buffer_unlink(jh);
 597         jh->b_cp_transaction = NULL;
 598
 599         if (transaction->t_checkpoint_list != NULL ||
 600             transaction->t_checkpoint_io_list != NULL)
 601                 goto out;
 602         JBUFFER_TRACE(jh, "transaction has no more buffers");
 603
 604         /*
 605          * There is one special case to worry about: if we have just pulled the
 606          * buffer off a running or committing transaction's checkpoing list,
 607          * then even if the checkpoint list is empty, the transaction obviously
 608          * cannot be dropped!
 609          *
 610          * The locking here around t_state is a bit sleazy.
 611          * See the comment at the end of journal_commit_transaction().
 612          */
 613         if (transaction->t_state != T_FINISHED) {
 614                 JBUFFER_TRACE(jh, "belongs to running/committing transaction");
 615                 goto out;
 616         }
 617
 618         /* OK, that was the last buffer for the transaction: we can now
 619            safely remove this transaction from the log */
 620
 621         __journal_drop_transaction(journal, transaction);
 622
 623         /* Just in case anybody was waiting for more transactions to be
 624            checkpointed... */
 625         wake_up(&journal->j_wait_logspace);
 626         ret = 1;
 627 out:
 628         JBUFFER_TRACE(jh, "exit");
 629         return ret;
 630 }
 631
 632 /*
 633  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 634  * list so that we know when it is safe to clean the transaction out of
 635  * the log.
 636  *
 637  * Called with the journal locked.
 638  * Called with j_list_lock held.
 639  */
 640 void __journal_insert_checkpoint(struct journal_head *jh,
 641                                transaction_t *transaction)
 642 {
 643         JBUFFER_TRACE(jh, "entry");
 644         J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 645         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 646
 647         jh->b_cp_transaction = transaction;
 648
 649         if (!transaction->t_checkpoint_list) {
 650                 jh->b_cpnext = jh->b_cpprev = jh;
 651         } else {
 652                 jh->b_cpnext = transaction->t_checkpoint_list;
 653                 jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
 654                 jh->b_cpprev->b_cpnext = jh;
 655                 jh->b_cpnext->b_cpprev = jh;
 656         }
 657         transaction->t_checkpoint_list = jh;
 658 }
 659
 660 /*
 661  * We've finished with this transaction structure: adios...
 662  *
 663  * The transaction must have no links except for the checkpoint by this
 664  * point.
 665  *
 666  * Called with the journal locked.
 667  * Called with j_list_lock held.
 668  */
 669
 670 void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 671 {
 672         assert_spin_locked(&journal->j_list_lock);
 673         if (transaction->t_cpnext) {
 674                 transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
 675                 transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
 676                 if (journal->j_checkpoint_transactions == transaction)
 677                         journal->j_checkpoint_transactions =
 678                                 transaction->t_cpnext;
 679                 if (journal->j_checkpoint_transactions == transaction)
 680                         journal->j_checkpoint_transactions = NULL;
 681         }
 682
 683         J_ASSERT(transaction->t_state == T_FINISHED);
 684         J_ASSERT(transaction->t_buffers == NULL);
 685         J_ASSERT(transaction->t_sync_datalist == NULL);
 686         J_ASSERT(transaction->t_forget == NULL);
 687         J_ASSERT(transaction->t_iobuf_list == NULL);
 688         J_ASSERT(transaction->t_shadow_list == NULL);
 689         J_ASSERT(transaction->t_log_list == NULL);
 690         J_ASSERT(transaction->t_checkpoint_list == NULL);
 691         J_ASSERT(transaction->t_checkpoint_io_list == NULL);
 692         J_ASSERT(transaction->t_updates == 0);
 693         J_ASSERT(journal->j_committing_transaction != transaction);
 694         J_ASSERT(journal->j_running_transaction != transaction);
 695
 696         jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
 697         kfree(transaction);
 698 }