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                 /*
 100                  * Get our reference so that bh cannot be freed before
 101                  * we unlock it
 102                  */
 103                 get_bh(bh);
 104                 JBUFFER_TRACE(jh, "remove from checkpoint list");
 105                 ret = __jbd2_journal_remove_checkpoint(jh) + 1;
 106                 BUFFER_TRACE(bh, "release");
 107                 __brelse(bh);
 108         }
 109         return ret;
 110 }
 111
 112 /*
 113  * __jbd2_log_wait_for_space: wait until there is space in the journal.
 114  *
 115  * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 116  * for a checkpoint to free up some space in the log.
 117  */
 118 void __jbd2_log_wait_for_space(journal_t *journal)
 119 {
 120         int nblocks, space_left;
 121         /* assert_spin_locked(&journal->j_state_lock); */
 122
 123         nblocks = jbd2_space_needed(journal);
 124         while (jbd2_log_space_left(journal) < nblocks) {
 125                 if (journal->j_flags & JBD2_ABORT)
 126                         return;
 127                 write_unlock(&journal->j_state_lock);
 128                 mutex_lock(&journal->j_checkpoint_mutex);
 129
 130                 /*
 131                  * Test again, another process may have checkpointed while we
 132                  * were waiting for the checkpoint lock. If there are no
 133                  * transactions ready to be checkpointed, try to recover
 134                  * journal space by calling cleanup_journal_tail(), and if
 135                  * that doesn't work, by waiting for the currently committing
 136                  * transaction to complete.  If there is absolutely no way
 137                  * to make progress, this is either a BUG or corrupted
 138                  * filesystem, so abort the journal and leave a stack
 139                  * trace for forensic evidence.
 140                  */
 141                 write_lock(&journal->j_state_lock);
 142                 spin_lock(&journal->j_list_lock);
 143                 nblocks = jbd2_space_needed(journal);
 144                 space_left = jbd2_log_space_left(journal);
 145                 if (space_left < nblocks) {
 146                         int chkpt = journal->j_checkpoint_transactions != NULL;
 147                         tid_t tid = 0;
 148
 149                         if (journal->j_committing_transaction)
 150                                 tid = journal->j_committing_transaction->t_tid;
 151                         spin_unlock(&journal->j_list_lock);
 152                         write_unlock(&journal->j_state_lock);
 153                         if (chkpt) {
 154                                 jbd2_log_do_checkpoint(journal);
 155                         } else if (jbd2_cleanup_journal_tail(journal) == 0) {
 156                                 /* We were able to recover space; yay! */
 157                                 ;
 158                         } else if (tid) {
 159                                 /*
 160                                  * jbd2_journal_commit_transaction() may want
 161                                  * to take the checkpoint_mutex if JBD2_FLUSHED
 162                                  * is set.  So we need to temporarily drop it.
 163                                  */
 164                                 mutex_unlock(&journal->j_checkpoint_mutex);
 165                                 jbd2_log_wait_commit(journal, tid);
 166                                 write_lock(&journal->j_state_lock);
 167                                 continue;
 168                         } else {
 169                                 printk(KERN_ERR "%s: needed %d blocks and "
 170                                        "only had %d space available\n",
 171                                        __func__, nblocks, space_left);
 172                                 printk(KERN_ERR "%s: no way to get more "
 173                                        "journal space in %s\n", __func__,
 174                                        journal->j_devname);
 175                                 WARN_ON(1);
 176                                 jbd2_journal_abort(journal, 0);
 177                         }
 178                         write_lock(&journal->j_state_lock);
 179                 } else {
 180                         spin_unlock(&journal->j_list_lock);
 181                 }
 182                 mutex_unlock(&journal->j_checkpoint_mutex);
 183         }
 184 }
 185
 186 /*
 187  * Clean up transaction's list of buffers submitted for io.
 188  * We wait for any pending IO to complete and remove any clean
 189  * buffers. Note that we take the buffers in the opposite ordering
 190  * from the one in which they were submitted for IO.
 191  *
 192  * Return 0 on success, and return <0 if some buffers have failed
 193  * to be written out.
 194  *
 195  * Called with j_list_lock held.
 196  */
 197 static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
 198 {
 199         struct journal_head *jh;
 200         struct buffer_head *bh;
 201         tid_t this_tid;
 202         int released = 0;
 203         int ret = 0;
 204
 205         this_tid = transaction->t_tid;
 206 restart:
 207         /* Did somebody clean up the transaction in the meanwhile? */
 208         if (journal->j_checkpoint_transactions != transaction ||
 209                         transaction->t_tid != this_tid)
 210                 return ret;
 211         while (!released && transaction->t_checkpoint_io_list) {
 212                 jh = transaction->t_checkpoint_io_list;
 213                 bh = jh2bh(jh);
 214                 get_bh(bh);
 215                 if (buffer_locked(bh)) {
 216                         spin_unlock(&journal->j_list_lock);
 217                         wait_on_buffer(bh);
 218                         /* the journal_head may have gone by now */
 219                         BUFFER_TRACE(bh, "brelse");
 220                         __brelse(bh);
 221                         spin_lock(&journal->j_list_lock);
 222                         goto restart;
 223                 }
 224                 if (unlikely(buffer_write_io_error(bh)))
 225                         ret = -EIO;
 226
 227                 /*
 228                  * Now in whatever state the buffer currently is, we know that
 229                  * it has been written out and so we can drop it from the list
 230                  */
 231                 released = __jbd2_journal_remove_checkpoint(jh);
 232                 __brelse(bh);
 233         }
 234
 235         return ret;
 236 }
 237
 238 static void
 239 __flush_batch(journal_t *journal, int *batch_count)
 240 {
 241         int i;
 242         struct blk_plug plug;
 243
 244         blk_start_plug(&plug);
 245         for (i = 0; i < *batch_count; i++)
 246                 write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE_SYNC);
 247         blk_finish_plug(&plug);
 248
 249         for (i = 0; i < *batch_count; i++) {
 250                 struct buffer_head *bh = journal->j_chkpt_bhs[i];
 251                 BUFFER_TRACE(bh, "brelse");
 252                 __brelse(bh);
 253         }
 254         *batch_count = 0;
 255 }
 256
 257 /*
 258  * Try to flush one buffer from the checkpoint list to disk.
 259  *
 260  * Return 1 if something happened which requires us to abort the current
 261  * scan of the checkpoint list.  Return <0 if the buffer has failed to
 262  * be written out.
 263  *
 264  * Called with j_list_lock held and drops it if 1 is returned
 265  */
 266 static int __process_buffer(journal_t *journal, struct journal_head *jh,
 267                             int *batch_count, transaction_t *transaction)
 268 {
 269         struct buffer_head *bh = jh2bh(jh);
 270         int ret = 0;
 271
 272         if (buffer_locked(bh)) {
 273                 get_bh(bh);
 274                 spin_unlock(&journal->j_list_lock);
 275                 wait_on_buffer(bh);
 276                 /* the journal_head may have gone by now */
 277                 BUFFER_TRACE(bh, "brelse");
 278                 __brelse(bh);
 279                 ret = 1;
 280         } else if (jh->b_transaction != NULL) {
 281                 transaction_t *t = jh->b_transaction;
 282                 tid_t tid = t->t_tid;
 283
 284                 transaction->t_chp_stats.cs_forced_to_close++;
 285                 spin_unlock(&journal->j_list_lock);
 286                 if (unlikely(journal->j_flags & JBD2_UNMOUNT))
 287                         /*
 288                          * The journal thread is dead; so starting and
 289                          * waiting for a commit to finish will cause
 290                          * us to wait for a _very_ long time.
 291                          */
 292                         printk(KERN_ERR "JBD2: %s: "
 293                                "Waiting for Godot: block %llu\n",
 294                                journal->j_devname,
 295                                (unsigned long long) bh->b_blocknr);
 296                 jbd2_log_start_commit(journal, tid);
 297                 jbd2_log_wait_commit(journal, tid);
 298                 ret = 1;
 299         } else if (!buffer_dirty(bh)) {
 300                 ret = 1;
 301                 if (unlikely(buffer_write_io_error(bh)))
 302                         ret = -EIO;
 303                 get_bh(bh);
 304                 BUFFER_TRACE(bh, "remove from checkpoint");
 305                 __jbd2_journal_remove_checkpoint(jh);
 306                 spin_unlock(&journal->j_list_lock);
 307                 __brelse(bh);
 308         } else {
 309                 /*
 310                  * Important: we are about to write the buffer, and
 311                  * possibly block, while still holding the journal lock.
 312                  * We cannot afford to let the transaction logic start
 313                  * messing around with this buffer before we write it to
 314                  * disk, as that would break recoverability.
 315                  */
 316                 BUFFER_TRACE(bh, "queue");
 317                 get_bh(bh);
 318                 J_ASSERT_BH(bh, !buffer_jwrite(bh));
 319                 journal->j_chkpt_bhs[*batch_count] = bh;
 320                 __buffer_relink_io(jh);
 321                 transaction->t_chp_stats.cs_written++;
 322                 (*batch_count)++;
 323                 if (*batch_count == JBD2_NR_BATCH) {
 324                         spin_unlock(&journal->j_list_lock);
 325                         __flush_batch(journal, batch_count);
 326                         ret = 1;
 327                 }
 328         }
 329         return ret;
 330 }
 331
 332 /*
 333  * Perform an actual checkpoint. We take the first transaction on the
 334  * list of transactions to be checkpointed and send all its buffers
 335  * to disk. We submit larger chunks of data at once.
 336  *
 337  * The journal should be locked before calling this function.
 338  * Called with j_checkpoint_mutex held.
 339  */
 340 int jbd2_log_do_checkpoint(journal_t *journal)
 341 {
 342         transaction_t *transaction;
 343         tid_t this_tid;
 344         int result;
 345
 346         jbd_debug(1, "Start checkpoint\n");
 347
 348         /*
 349          * First thing: if there are any transactions in the log which
 350          * don't need checkpointing, just eliminate them from the
 351          * journal straight away.
 352          */
 353         result = jbd2_cleanup_journal_tail(journal);
 354         trace_jbd2_checkpoint(journal, result);
 355         jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
 356         if (result <= 0)
 357                 return result;
 358
 359         /*
 360          * OK, we need to start writing disk blocks.  Take one transaction
 361          * and write it.
 362          */
 363         result = 0;
 364         spin_lock(&journal->j_list_lock);
 365         if (!journal->j_checkpoint_transactions)
 366                 goto out;
 367         transaction = journal->j_checkpoint_transactions;
 368         if (transaction->t_chp_stats.cs_chp_time == 0)
 369                 transaction->t_chp_stats.cs_chp_time = jiffies;
 370         this_tid = transaction->t_tid;
 371 restart:
 372         /*
 373          * If someone cleaned up this transaction while we slept, we're
 374          * done (maybe it's a new transaction, but it fell at the same
 375          * address).
 376          */
 377         if (journal->j_checkpoint_transactions == transaction &&
 378                         transaction->t_tid == this_tid) {
 379                 int batch_count = 0;
 380                 struct journal_head *jh;
 381                 int retry = 0, err;
 382
 383                 while (!retry && transaction->t_checkpoint_list) {
 384                         jh = transaction->t_checkpoint_list;
 385                         retry = __process_buffer(journal, jh, &batch_count,
 386                                                  transaction);
 387                         if (retry < 0 && !result)
 388                                 result = retry;
 389                         if (!retry && (need_resched() ||
 390                                 spin_needbreak(&journal->j_list_lock))) {
 391                                 spin_unlock(&journal->j_list_lock);
 392                                 retry = 1;
 393                                 break;
 394                         }
 395                 }
 396
 397                 if (batch_count) {
 398                         if (!retry) {
 399                                 spin_unlock(&journal->j_list_lock);
 400                                 retry = 1;
 401                         }
 402                         __flush_batch(journal, &batch_count);
 403                 }
 404
 405                 if (retry) {
 406                         spin_lock(&journal->j_list_lock);
 407                         goto restart;
 408                 }
 409                 /*
 410                  * Now we have cleaned up the first transaction's checkpoint
 411                  * list. Let's clean up the second one
 412                  */
 413                 err = __wait_cp_io(journal, transaction);
 414                 if (!result)
 415                         result = err;
 416         }
 417 out:
 418         spin_unlock(&journal->j_list_lock);
 419         if (result < 0)
 420                 jbd2_journal_abort(journal, result);
 421         else
 422                 result = jbd2_cleanup_journal_tail(journal);
 423
 424         return (result < 0) ? result : 0;
 425 }
 426
 427 /*
 428  * Check the list of checkpoint transactions for the journal to see if
 429  * we have already got rid of any since the last update of the log tail
 430  * in the journal superblock.  If so, we can instantly roll the
 431  * superblock forward to remove those transactions from the log.
 432  *
 433  * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 434  *
 435  * Called with the journal lock held.
 436  *
 437  * This is the only part of the journaling code which really needs to be
 438  * aware of transaction aborts.  Checkpointing involves writing to the
 439  * main filesystem area rather than to the journal, so it can proceed
 440  * even in abort state, but we must not update the super block if
 441  * checkpointing may have failed.  Otherwise, we would lose some metadata
 442  * buffers which should be written-back to the filesystem.
 443  */
 444
 445 int jbd2_cleanup_journal_tail(journal_t *journal)
 446 {
 447         tid_t           first_tid;
 448         unsigned long   blocknr;
 449
 450         if (is_journal_aborted(journal))
 451                 return 1;
 452
 453         if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
 454                 return 1;
 455         J_ASSERT(blocknr != 0);
 456
 457         /*
 458          * We need to make sure that any blocks that were recently written out
 459          * --- perhaps by jbd2_log_do_checkpoint() --- are flushed out before
 460          * we drop the transactions from the journal. It's unlikely this will
 461          * be necessary, especially with an appropriately sized journal, but we
 462          * need this to guarantee correctness.  Fortunately
 463          * jbd2_cleanup_journal_tail() doesn't get called all that often.
 464          */
 465         if (journal->j_flags & JBD2_BARRIER)
 466                 blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
 467
 468         __jbd2_update_log_tail(journal, first_tid, blocknr);
 469         return 0;
 470 }
 471
 472
 473 /* Checkpoint list management */
 474
 475 /*
 476  * journal_clean_one_cp_list
 477  *
 478  * Find all the written-back checkpoint buffers in the given list and
 479  * release them.
 480  *
 481  * Called with the journal locked.
 482  * Called with j_list_lock held.
 483  * Returns number of buffers reaped (for debug)
 484  */
 485
 486 static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
 487 {
 488         struct journal_head *last_jh;
 489         struct journal_head *next_jh = jh;
 490         int ret, freed = 0;
 491
 492         *released = 0;
 493         if (!jh)
 494                 return 0;
 495
 496         last_jh = jh->b_cpprev;
 497         do {
 498                 jh = next_jh;
 499                 next_jh = jh->b_cpnext;
 500                 ret = __try_to_free_cp_buf(jh);
 501                 if (ret) {
 502                         freed++;
 503                         if (ret == 2) {
 504                                 *released = 1;
 505                                 return freed;
 506                         }
 507                 }
 508                 /*
 509                  * This function only frees up some memory
 510                  * if possible so we dont have an obligation
 511                  * to finish processing. Bail out if preemption
 512                  * requested:
 513                  */
 514                 if (need_resched())
 515                         return freed;
 516         } while (jh != last_jh);
 517
 518         return freed;
 519 }
 520
 521 /*
 522  * journal_clean_checkpoint_list
 523  *
 524  * Find all the written-back checkpoint buffers in the journal and release them.
 525  *
 526  * Called with the journal locked.
 527  * Called with j_list_lock held.
 528  * Returns number of buffers reaped (for debug)
 529  */
 530
 531 int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
 532 {
 533         transaction_t *transaction, *last_transaction, *next_transaction;
 534         int ret = 0;
 535         int released;
 536
 537         transaction = journal->j_checkpoint_transactions;
 538         if (!transaction)
 539                 goto out;
 540
 541         last_transaction = transaction->t_cpprev;
 542         next_transaction = transaction;
 543         do {
 544                 transaction = next_transaction;
 545                 next_transaction = transaction->t_cpnext;
 546                 ret += journal_clean_one_cp_list(transaction->
 547                                 t_checkpoint_list, &released);
 548                 /*
 549                  * This function only frees up some memory if possible so we
 550                  * dont have an obligation to finish processing. Bail out if
 551                  * preemption requested:
 552                  */
 553                 if (need_resched())
 554                         goto out;
 555                 if (released)
 556                         continue;
 557                 /*
 558                  * It is essential that we are as careful as in the case of
 559                  * t_checkpoint_list with removing the buffer from the list as
 560                  * we can possibly see not yet submitted buffers on io_list
 561                  */
 562                 ret += journal_clean_one_cp_list(transaction->
 563                                 t_checkpoint_io_list, &released);
 564                 if (need_resched())
 565                         goto out;
 566         } while (transaction != last_transaction);
 567 out:
 568         return ret;
 569 }
 570
 571 /*
 572  * journal_remove_checkpoint: called after a buffer has been committed
 573  * to disk (either by being write-back flushed to disk, or being
 574  * committed to the log).
 575  *
 576  * We cannot safely clean a transaction out of the log until all of the
 577  * buffer updates committed in that transaction have safely been stored
 578  * elsewhere on disk.  To achieve this, all of the buffers in a
 579  * transaction need to be maintained on the transaction's checkpoint
 580  * lists until they have been rewritten, at which point this function is
 581  * called to remove the buffer from the existing transaction's
 582  * checkpoint lists.
 583  *
 584  * The function returns 1 if it frees the transaction, 0 otherwise.
 585  * The function can free jh and bh.
 586  *
 587  * This function is called with j_list_lock held.
 588  */
 589 int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 590 {
 591         struct transaction_chp_stats_s *stats;
 592         transaction_t *transaction;
 593         journal_t *journal;
 594         int ret = 0;
 595
 596         JBUFFER_TRACE(jh, "entry");
 597
 598         if ((transaction = jh->b_cp_transaction) == NULL) {
 599                 JBUFFER_TRACE(jh, "not on transaction");
 600                 goto out;
 601         }
 602         journal = transaction->t_journal;
 603
 604         JBUFFER_TRACE(jh, "removing from transaction");
 605         __buffer_unlink(jh);
 606         jh->b_cp_transaction = NULL;
 607         jbd2_journal_put_journal_head(jh);
 608
 609         if (transaction->t_checkpoint_list != NULL ||
 610             transaction->t_checkpoint_io_list != NULL)
 611                 goto out;
 612
 613         /*
 614          * There is one special case to worry about: if we have just pulled the
 615          * buffer off a running or committing transaction's checkpoing list,
 616          * then even if the checkpoint list is empty, the transaction obviously
 617          * cannot be dropped!
 618          *
 619          * The locking here around t_state is a bit sleazy.
 620          * See the comment at the end of jbd2_journal_commit_transaction().
 621          */
 622         if (transaction->t_state != T_FINISHED)
 623                 goto out;
 624
 625         /* OK, that was the last buffer for the transaction: we can now
 626            safely remove this transaction from the log */
 627         stats = &transaction->t_chp_stats;
 628         if (stats->cs_chp_time)
 629                 stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
 630                                                     jiffies);
 631         trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
 632                                     transaction->t_tid, stats);
 633
 634         __jbd2_journal_drop_transaction(journal, transaction);
 635         jbd2_journal_free_transaction(transaction);
 636         ret = 1;
 637 out:
 638         return ret;
 639 }
 640
 641 /*
 642  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 643  * list so that we know when it is safe to clean the transaction out of
 644  * the log.
 645  *
 646  * Called with the journal locked.
 647  * Called with j_list_lock held.
 648  */
 649 void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
 650                                transaction_t *transaction)
 651 {
 652         JBUFFER_TRACE(jh, "entry");
 653         J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 654         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 655
 656         /* Get reference for checkpointing transaction */
 657         jbd2_journal_grab_journal_head(jh2bh(jh));
 658         jh->b_cp_transaction = transaction;
 659
 660         if (!transaction->t_checkpoint_list) {
 661                 jh->b_cpnext = jh->b_cpprev = jh;
 662         } else {
 663                 jh->b_cpnext = transaction->t_checkpoint_list;
 664                 jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
 665                 jh->b_cpprev->b_cpnext = jh;
 666                 jh->b_cpnext->b_cpprev = jh;
 667         }
 668         transaction->t_checkpoint_list = jh;
 669 }
 670
 671 /*
 672  * We've finished with this transaction structure: adios...
 673  *
 674  * The transaction must have no links except for the checkpoint by this
 675  * point.
 676  *
 677  * Called with the journal locked.
 678  * Called with j_list_lock held.
 679  */
 680
 681 void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 682 {
 683         assert_spin_locked(&journal->j_list_lock);
 684         if (transaction->t_cpnext) {
 685                 transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
 686                 transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
 687                 if (journal->j_checkpoint_transactions == transaction)
 688                         journal->j_checkpoint_transactions =
 689                                 transaction->t_cpnext;
 690                 if (journal->j_checkpoint_transactions == transaction)
 691                         journal->j_checkpoint_transactions = NULL;
 692         }
 693
 694         J_ASSERT(transaction->t_state == T_FINISHED);
 695         J_ASSERT(transaction->t_buffers == NULL);
 696         J_ASSERT(transaction->t_forget == NULL);
 697         J_ASSERT(transaction->t_shadow_list == NULL);
 698         J_ASSERT(transaction->t_checkpoint_list == NULL);
 699         J_ASSERT(transaction->t_checkpoint_io_list == NULL);
 700         J_ASSERT(atomic_read(&transaction->t_updates) == 0);
 701         J_ASSERT(journal->j_committing_transaction != transaction);
 702         J_ASSERT(journal->j_running_transaction != transaction);
 703
 704         trace_jbd2_drop_transaction(journal, transaction);
 705
 706         jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
 707 }