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  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
  92  */
  93 static int __try_to_free_cp_buf(struct journal_head *jh)
  94 {
  95         int ret = 0;
  96         struct buffer_head *bh = jh2bh(jh);
  97
  98         if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
  99             !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
 100                 /*
 101                  * Get our reference so that bh cannot be freed before
 102                  * we unlock it
 103                  */
 104                 get_bh(bh);
 105                 JBUFFER_TRACE(jh, "remove from checkpoint list");
 106                 ret = __jbd2_journal_remove_checkpoint(jh) + 1;
 107                 jbd_unlock_bh_state(bh);
 108                 BUFFER_TRACE(bh, "release");
 109                 __brelse(bh);
 110         } else {
 111                 jbd_unlock_bh_state(bh);
 112         }
 113         return ret;
 114 }
 115
 116 /*
 117  * __jbd2_log_wait_for_space: wait until there is space in the journal.
 118  *
 119  * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 120  * for a checkpoint to free up some space in the log.
 121  */
 122 void __jbd2_log_wait_for_space(journal_t *journal)
 123 {
 124         int nblocks, space_left;
 125         /* assert_spin_locked(&journal->j_state_lock); */
 126
 127         nblocks = jbd_space_needed(journal);
 128         while (__jbd2_log_space_left(journal) < nblocks) {
 129                 if (journal->j_flags & JBD2_ABORT)
 130                         return;
 131                 write_unlock(&journal->j_state_lock);
 132                 mutex_lock(&journal->j_checkpoint_mutex);
 133
 134                 /*
 135                  * Test again, another process may have checkpointed while we
 136                  * were waiting for the checkpoint lock. If there are no
 137                  * transactions ready to be checkpointed, try to recover
 138                  * journal space by calling cleanup_journal_tail(), and if
 139                  * that doesn't work, by waiting for the currently committing
 140                  * transaction to complete.  If there is absolutely no way
 141                  * to make progress, this is either a BUG or corrupted
 142                  * filesystem, so abort the journal and leave a stack
 143                  * trace for forensic evidence.
 144                  */
 145                 write_lock(&journal->j_state_lock);
 146                 spin_lock(&journal->j_list_lock);
 147                 nblocks = jbd_space_needed(journal);
 148                 space_left = __jbd2_log_space_left(journal);
 149                 if (space_left < nblocks) {
 150                         int chkpt = journal->j_checkpoint_transactions != NULL;
 151                         tid_t tid = 0;
 152
 153                         if (journal->j_committing_transaction)
 154                                 tid = journal->j_committing_transaction->t_tid;
 155                         spin_unlock(&journal->j_list_lock);
 156                         write_unlock(&journal->j_state_lock);
 157                         if (chkpt) {
 158                                 jbd2_log_do_checkpoint(journal);
 159                         } else if (jbd2_cleanup_journal_tail(journal) == 0) {
 160                                 /* We were able to recover space; yay! */
 161                                 ;
 162                         } else if (tid) {
 163                                 jbd2_log_wait_commit(journal, tid);
 164                         } else {
 165                                 printk(KERN_ERR "%s: needed %d blocks and "
 166                                        "only had %d space available\n",
 167                                        __func__, nblocks, space_left);
 168                                 printk(KERN_ERR "%s: no way to get more "
 169                                        "journal space in %s\n", __func__,
 170                                        journal->j_devname);
 171                                 WARN_ON(1);
 172                                 jbd2_journal_abort(journal, 0);
 173                         }
 174                         write_lock(&journal->j_state_lock);
 175                 } else {
 176                         spin_unlock(&journal->j_list_lock);
 177                 }
 178                 mutex_unlock(&journal->j_checkpoint_mutex);
 179         }
 180 }
 181
 182 /*
 183  * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 184  * The caller must restart a list walk.  Wait for someone else to run
 185  * jbd_unlock_bh_state().
 186  */
 187 static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
 188         __releases(journal->j_list_lock)
 189 {
 190         get_bh(bh);
 191         spin_unlock(&journal->j_list_lock);
 192         jbd_lock_bh_state(bh);
 193         jbd_unlock_bh_state(bh);
 194         put_bh(bh);
 195 }
 196
 197 /*
 198  * Clean up transaction's list of buffers submitted for io.
 199  * We wait for any pending IO to complete and remove any clean
 200  * buffers. Note that we take the buffers in the opposite ordering
 201  * from the one in which they were submitted for IO.
 202  *
 203  * Return 0 on success, and return <0 if some buffers have failed
 204  * to be written out.
 205  *
 206  * Called with j_list_lock held.
 207  */
 208 static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
 209 {
 210         struct journal_head *jh;
 211         struct buffer_head *bh;
 212         tid_t this_tid;
 213         int released = 0;
 214         int ret = 0;
 215
 216         this_tid = transaction->t_tid;
 217 restart:
 218         /* Did somebody clean up the transaction in the meanwhile? */
 219         if (journal->j_checkpoint_transactions != transaction ||
 220                         transaction->t_tid != this_tid)
 221                 return ret;
 222         while (!released && transaction->t_checkpoint_io_list) {
 223                 jh = transaction->t_checkpoint_io_list;
 224                 bh = jh2bh(jh);
 225                 if (!jbd_trylock_bh_state(bh)) {
 226                         jbd_sync_bh(journal, bh);
 227                         spin_lock(&journal->j_list_lock);
 228                         goto restart;
 229                 }
 230                 get_bh(bh);
 231                 if (buffer_locked(bh)) {
 232                         spin_unlock(&journal->j_list_lock);
 233                         jbd_unlock_bh_state(bh);
 234                         wait_on_buffer(bh);
 235                         /* the journal_head may have gone by now */
 236                         BUFFER_TRACE(bh, "brelse");
 237                         __brelse(bh);
 238                         spin_lock(&journal->j_list_lock);
 239                         goto restart;
 240                 }
 241                 if (unlikely(buffer_write_io_error(bh)))
 242                         ret = -EIO;
 243
 244                 /*
 245                  * Now in whatever state the buffer currently is, we know that
 246                  * it has been written out and so we can drop it from the list
 247                  */
 248                 released = __jbd2_journal_remove_checkpoint(jh);
 249                 jbd_unlock_bh_state(bh);
 250                 __brelse(bh);
 251         }
 252
 253         return ret;
 254 }
 255
 256 static void
 257 __flush_batch(journal_t *journal, int *batch_count)
 258 {
 259         int i;
 260         struct blk_plug plug;
 261
 262         blk_start_plug(&plug);
 263         for (i = 0; i < *batch_count; i++)
 264                 write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE_SYNC);
 265         blk_finish_plug(&plug);
 266
 267         for (i = 0; i < *batch_count; i++) {
 268                 struct buffer_head *bh = journal->j_chkpt_bhs[i];
 269                 clear_buffer_jwrite(bh);
 270                 BUFFER_TRACE(bh, "brelse");
 271                 __brelse(bh);
 272         }
 273         *batch_count = 0;
 274 }
 275
 276 /*
 277  * Try to flush one buffer from the checkpoint list to disk.
 278  *
 279  * Return 1 if something happened which requires us to abort the current
 280  * scan of the checkpoint list.  Return <0 if the buffer has failed to
 281  * be written out.
 282  *
 283  * Called with j_list_lock held and drops it if 1 is returned
 284  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 285  */
 286 static int __process_buffer(journal_t *journal, struct journal_head *jh,
 287                             int *batch_count, transaction_t *transaction)
 288 {
 289         struct buffer_head *bh = jh2bh(jh);
 290         int ret = 0;
 291
 292         if (buffer_locked(bh)) {
 293                 get_bh(bh);
 294                 spin_unlock(&journal->j_list_lock);
 295                 jbd_unlock_bh_state(bh);
 296                 wait_on_buffer(bh);
 297                 /* the journal_head may have gone by now */
 298                 BUFFER_TRACE(bh, "brelse");
 299                 __brelse(bh);
 300                 ret = 1;
 301         } else if (jh->b_transaction != NULL) {
 302                 transaction_t *t = jh->b_transaction;
 303                 tid_t tid = t->t_tid;
 304
 305                 transaction->t_chp_stats.cs_forced_to_close++;
 306                 spin_unlock(&journal->j_list_lock);
 307                 jbd_unlock_bh_state(bh);
 308                 if (unlikely(journal->j_flags & JBD2_UNMOUNT))
 309                         /*
 310                          * The journal thread is dead; so starting and
 311                          * waiting for a commit to finish will cause
 312                          * us to wait for a _very_ long time.
 313                          */
 314                         printk(KERN_ERR "JBD2: %s: "
 315                                "Waiting for Godot: block %llu\n",
 316                                journal->j_devname,
 317                                (unsigned long long) bh->b_blocknr);
 318                 jbd2_log_start_commit(journal, tid);
 319                 jbd2_log_wait_commit(journal, tid);
 320                 ret = 1;
 321         } else if (!buffer_dirty(bh)) {
 322                 ret = 1;
 323                 if (unlikely(buffer_write_io_error(bh)))
 324                         ret = -EIO;
 325                 get_bh(bh);
 326                 J_ASSERT_JH(jh, !buffer_jbddirty(bh));
 327                 BUFFER_TRACE(bh, "remove from checkpoint");
 328                 __jbd2_journal_remove_checkpoint(jh);
 329                 spin_unlock(&journal->j_list_lock);
 330                 jbd_unlock_bh_state(bh);
 331                 __brelse(bh);
 332         } else {
 333                 /*
 334                  * Important: we are about to write the buffer, and
 335                  * possibly block, while still holding the journal lock.
 336                  * We cannot afford to let the transaction logic start
 337                  * messing around with this buffer before we write it to
 338                  * disk, as that would break recoverability.
 339                  */
 340                 BUFFER_TRACE(bh, "queue");
 341                 get_bh(bh);
 342                 J_ASSERT_BH(bh, !buffer_jwrite(bh));
 343                 set_buffer_jwrite(bh);
 344                 journal->j_chkpt_bhs[*batch_count] = bh;
 345                 __buffer_relink_io(jh);
 346                 jbd_unlock_bh_state(bh);
 347                 transaction->t_chp_stats.cs_written++;
 348                 (*batch_count)++;
 349                 if (*batch_count == JBD2_NR_BATCH) {
 350                         spin_unlock(&journal->j_list_lock);
 351                         __flush_batch(journal, batch_count);
 352                         ret = 1;
 353                 }
 354         }
 355         return ret;
 356 }
 357
 358 /*
 359  * Perform an actual checkpoint. We take the first transaction on the
 360  * list of transactions to be checkpointed and send all its buffers
 361  * to disk. We submit larger chunks of data at once.
 362  *
 363  * The journal should be locked before calling this function.
 364  * Called with j_checkpoint_mutex held.
 365  */
 366 int jbd2_log_do_checkpoint(journal_t *journal)
 367 {
 368         transaction_t *transaction;
 369         tid_t this_tid;
 370         int result;
 371
 372         jbd_debug(1, "Start checkpoint\n");
 373
 374         /*
 375          * First thing: if there are any transactions in the log which
 376          * don't need checkpointing, just eliminate them from the
 377          * journal straight away.
 378          */
 379         result = jbd2_cleanup_journal_tail(journal);
 380         trace_jbd2_checkpoint(journal, result);
 381         jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
 382         if (result <= 0)
 383                 return result;
 384
 385         /*
 386          * OK, we need to start writing disk blocks.  Take one transaction
 387          * and write it.
 388          */
 389         result = 0;
 390         spin_lock(&journal->j_list_lock);
 391         if (!journal->j_checkpoint_transactions)
 392                 goto out;
 393         transaction = journal->j_checkpoint_transactions;
 394         if (transaction->t_chp_stats.cs_chp_time == 0)
 395                 transaction->t_chp_stats.cs_chp_time = jiffies;
 396         this_tid = transaction->t_tid;
 397 restart:
 398         /*
 399          * If someone cleaned up this transaction while we slept, we're
 400          * done (maybe it's a new transaction, but it fell at the same
 401          * address).
 402          */
 403         if (journal->j_checkpoint_transactions == transaction &&
 404                         transaction->t_tid == this_tid) {
 405                 int batch_count = 0;
 406                 struct journal_head *jh;
 407                 int retry = 0, err;
 408
 409                 while (!retry && transaction->t_checkpoint_list) {
 410                         struct buffer_head *bh;
 411
 412                         jh = transaction->t_checkpoint_list;
 413                         bh = jh2bh(jh);
 414                         if (!jbd_trylock_bh_state(bh)) {
 415                                 jbd_sync_bh(journal, bh);
 416                                 retry = 1;
 417                                 break;
 418                         }
 419                         retry = __process_buffer(journal, jh, &batch_count,
 420                                                  transaction);
 421                         if (retry < 0 && !result)
 422                                 result = retry;
 423                         if (!retry && (need_resched() ||
 424                                 spin_needbreak(&journal->j_list_lock))) {
 425                                 spin_unlock(&journal->j_list_lock);
 426                                 retry = 1;
 427                                 break;
 428                         }
 429                 }
 430
 431                 if (batch_count) {
 432                         if (!retry) {
 433                                 spin_unlock(&journal->j_list_lock);
 434                                 retry = 1;
 435                         }
 436                         __flush_batch(journal, &batch_count);
 437                 }
 438
 439                 if (retry) {
 440                         spin_lock(&journal->j_list_lock);
 441                         goto restart;
 442                 }
 443                 /*
 444                  * Now we have cleaned up the first transaction's checkpoint
 445                  * list. Let's clean up the second one
 446                  */
 447                 err = __wait_cp_io(journal, transaction);
 448                 if (!result)
 449                         result = err;
 450         }
 451 out:
 452         spin_unlock(&journal->j_list_lock);
 453         if (result < 0)
 454                 jbd2_journal_abort(journal, result);
 455         else
 456                 result = jbd2_cleanup_journal_tail(journal);
 457
 458         return (result < 0) ? result : 0;
 459 }
 460
 461 /*
 462  * Check the list of checkpoint transactions for the journal to see if
 463  * we have already got rid of any since the last update of the log tail
 464  * in the journal superblock.  If so, we can instantly roll the
 465  * superblock forward to remove those transactions from the log.
 466  *
 467  * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 468  *
 469  * Called with the journal lock held.
 470  *
 471  * This is the only part of the journaling code which really needs to be
 472  * aware of transaction aborts.  Checkpointing involves writing to the
 473  * main filesystem area rather than to the journal, so it can proceed
 474  * even in abort state, but we must not update the super block if
 475  * checkpointing may have failed.  Otherwise, we would lose some metadata
 476  * buffers which should be written-back to the filesystem.
 477  */
 478
 479 int jbd2_cleanup_journal_tail(journal_t *journal)
 480 {
 481         tid_t           first_tid;
 482         unsigned long   blocknr;
 483
 484         if (is_journal_aborted(journal))
 485                 return -EIO;
 486
 487         if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
 488                 return 1;
 489         J_ASSERT(blocknr != 0);
 490
 491         /*
 492          * We need to make sure that any blocks that were recently written out
 493          * --- perhaps by jbd2_log_do_checkpoint() --- are flushed out before
 494          * we drop the transactions from the journal. It's unlikely this will
 495          * be necessary, especially with an appropriately sized journal, but we
 496          * need this to guarantee correctness.  Fortunately
 497          * jbd2_cleanup_journal_tail() doesn't get called all that often.
 498          */
 499         if (journal->j_flags & JBD2_BARRIER)
 500                 blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL);
 501
 502         return __jbd2_update_log_tail(journal, first_tid, blocknr);
 503 }
 504
 505
 506 /* Checkpoint list management */
 507
 508 /*
 509  * journal_clean_one_cp_list
 510  *
 511  * Find all the written-back checkpoint buffers in the given list and
 512  * release them.
 513  *
 514  * Called with the journal locked.
 515  * Called with j_list_lock held.
 516  * Returns number of bufers reaped (for debug)
 517  */
 518
 519 static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
 520 {
 521         struct journal_head *last_jh;
 522         struct journal_head *next_jh = jh;
 523         int ret, freed = 0;
 524
 525         *released = 0;
 526         if (!jh)
 527                 return 0;
 528
 529         last_jh = jh->b_cpprev;
 530         do {
 531                 jh = next_jh;
 532                 next_jh = jh->b_cpnext;
 533                 /* Use trylock because of the ranking */
 534                 if (jbd_trylock_bh_state(jh2bh(jh))) {
 535                         ret = __try_to_free_cp_buf(jh);
 536                         if (ret) {
 537                                 freed++;
 538                                 if (ret == 2) {
 539                                         *released = 1;
 540                                         return freed;
 541                                 }
 542                         }
 543                 }
 544                 /*
 545                  * This function only frees up some memory
 546                  * if possible so we dont have an obligation
 547                  * to finish processing. Bail out if preemption
 548                  * requested:
 549                  */
 550                 if (need_resched())
 551                         return freed;
 552         } while (jh != last_jh);
 553
 554         return freed;
 555 }
 556
 557 /*
 558  * journal_clean_checkpoint_list
 559  *
 560  * Find all the written-back checkpoint buffers in the journal and release them.
 561  *
 562  * Called with the journal locked.
 563  * Called with j_list_lock held.
 564  * Returns number of buffers reaped (for debug)
 565  */
 566
 567 int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
 568 {
 569         transaction_t *transaction, *last_transaction, *next_transaction;
 570         int ret = 0;
 571         int released;
 572
 573         transaction = journal->j_checkpoint_transactions;
 574         if (!transaction)
 575                 goto out;
 576
 577         last_transaction = transaction->t_cpprev;
 578         next_transaction = transaction;
 579         do {
 580                 transaction = next_transaction;
 581                 next_transaction = transaction->t_cpnext;
 582                 ret += journal_clean_one_cp_list(transaction->
 583                                 t_checkpoint_list, &released);
 584                 /*
 585                  * This function only frees up some memory if possible so we
 586                  * dont have an obligation to finish processing. Bail out if
 587                  * preemption requested:
 588                  */
 589                 if (need_resched())
 590                         goto out;
 591                 if (released)
 592                         continue;
 593                 /*
 594                  * It is essential that we are as careful as in the case of
 595                  * t_checkpoint_list with removing the buffer from the list as
 596                  * we can possibly see not yet submitted buffers on io_list
 597                  */
 598                 ret += journal_clean_one_cp_list(transaction->
 599                                 t_checkpoint_io_list, &released);
 600                 if (need_resched())
 601                         goto out;
 602         } while (transaction != last_transaction);
 603 out:
 604         return ret;
 605 }
 606
 607 /*
 608  * journal_remove_checkpoint: called after a buffer has been committed
 609  * to disk (either by being write-back flushed to disk, or being
 610  * committed to the log).
 611  *
 612  * We cannot safely clean a transaction out of the log until all of the
 613  * buffer updates committed in that transaction have safely been stored
 614  * elsewhere on disk.  To achieve this, all of the buffers in a
 615  * transaction need to be maintained on the transaction's checkpoint
 616  * lists until they have been rewritten, at which point this function is
 617  * called to remove the buffer from the existing transaction's
 618  * checkpoint lists.
 619  *
 620  * The function returns 1 if it frees the transaction, 0 otherwise.
 621  * The function can free jh and bh.
 622  *
 623  * This function is called with j_list_lock held.
 624  * This function is called with jbd_lock_bh_state(jh2bh(jh))
 625  */
 626
 627 int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
 628 {
 629         struct transaction_chp_stats_s *stats;
 630         transaction_t *transaction;
 631         journal_t *journal;
 632         int ret = 0;
 633
 634         JBUFFER_TRACE(jh, "entry");
 635
 636         if ((transaction = jh->b_cp_transaction) == NULL) {
 637                 JBUFFER_TRACE(jh, "not on transaction");
 638                 goto out;
 639         }
 640         journal = transaction->t_journal;
 641
 642         JBUFFER_TRACE(jh, "removing from transaction");
 643         __buffer_unlink(jh);
 644         jh->b_cp_transaction = NULL;
 645         jbd2_journal_put_journal_head(jh);
 646
 647         if (transaction->t_checkpoint_list != NULL ||
 648             transaction->t_checkpoint_io_list != NULL)
 649                 goto out;
 650
 651         /*
 652          * There is one special case to worry about: if we have just pulled the
 653          * buffer off a running or committing transaction's checkpoing list,
 654          * then even if the checkpoint list is empty, the transaction obviously
 655          * cannot be dropped!
 656          *
 657          * The locking here around t_state is a bit sleazy.
 658          * See the comment at the end of jbd2_journal_commit_transaction().
 659          */
 660         if (transaction->t_state != T_FINISHED)
 661                 goto out;
 662
 663         /* OK, that was the last buffer for the transaction: we can now
 664            safely remove this transaction from the log */
 665         stats = &transaction->t_chp_stats;
 666         if (stats->cs_chp_time)
 667                 stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
 668                                                     jiffies);
 669         trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
 670                                     transaction->t_tid, stats);
 671
 672         __jbd2_journal_drop_transaction(journal, transaction);
 673         kfree(transaction);
 674
 675         /* Just in case anybody was waiting for more transactions to be
 676            checkpointed... */
 677         wake_up(&journal->j_wait_logspace);
 678         ret = 1;
 679 out:
 680         return ret;
 681 }
 682
 683 /*
 684  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 685  * list so that we know when it is safe to clean the transaction out of
 686  * the log.
 687  *
 688  * Called with the journal locked.
 689  * Called with j_list_lock held.
 690  */
 691 void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
 692                                transaction_t *transaction)
 693 {
 694         JBUFFER_TRACE(jh, "entry");
 695         J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 696         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 697
 698         /* Get reference for checkpointing transaction */
 699         jbd2_journal_grab_journal_head(jh2bh(jh));
 700         jh->b_cp_transaction = transaction;
 701
 702         if (!transaction->t_checkpoint_list) {
 703                 jh->b_cpnext = jh->b_cpprev = jh;
 704         } else {
 705                 jh->b_cpnext = transaction->t_checkpoint_list;
 706                 jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
 707                 jh->b_cpprev->b_cpnext = jh;
 708                 jh->b_cpnext->b_cpprev = jh;
 709         }
 710         transaction->t_checkpoint_list = jh;
 711 }
 712
 713 /*
 714  * We've finished with this transaction structure: adios...
 715  *
 716  * The transaction must have no links except for the checkpoint by this
 717  * point.
 718  *
 719  * Called with the journal locked.
 720  * Called with j_list_lock held.
 721  */
 722
 723 void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 724 {
 725         assert_spin_locked(&journal->j_list_lock);
 726         if (transaction->t_cpnext) {
 727                 transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
 728                 transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
 729                 if (journal->j_checkpoint_transactions == transaction)
 730                         journal->j_checkpoint_transactions =
 731                                 transaction->t_cpnext;
 732                 if (journal->j_checkpoint_transactions == transaction)
 733                         journal->j_checkpoint_transactions = NULL;
 734         }
 735
 736         J_ASSERT(transaction->t_state == T_FINISHED);
 737         J_ASSERT(transaction->t_buffers == NULL);
 738         J_ASSERT(transaction->t_forget == NULL);
 739         J_ASSERT(transaction->t_iobuf_list == NULL);
 740         J_ASSERT(transaction->t_shadow_list == NULL);
 741         J_ASSERT(transaction->t_log_list == NULL);
 742         J_ASSERT(transaction->t_checkpoint_list == NULL);
 743         J_ASSERT(transaction->t_checkpoint_io_list == NULL);
 744         J_ASSERT(atomic_read(&transaction->t_updates) == 0);
 745         J_ASSERT(journal->j_committing_transaction != transaction);
 746         J_ASSERT(journal->j_running_transaction != transaction);
 747
 748         jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
 749 }