linux/fs/jbd/checkpoint.c
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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#include <linux/blkdev.h>
  26#include <trace/events/jbd.h>
  27
  28/*
  29 * Unlink a buffer from a transaction checkpoint list.
  30 *
  31 * Called with j_list_lock held.
  32 */
  33static 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 */
  51static 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 */
  68static 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 */
  93static 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 = __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 * __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 */
 122void __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 (__log_space_left(journal) < nblocks) {
 129                if (journal->j_flags & JFS_ABORT)
 130                        return;
 131                spin_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                spin_lock(&journal->j_state_lock);
 146                spin_lock(&journal->j_list_lock);
 147                nblocks = jbd_space_needed(journal);
 148                space_left = __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                        spin_unlock(&journal->j_state_lock);
 157                        if (chkpt) {
 158                                log_do_checkpoint(journal);
 159                        } else if (cleanup_journal_tail(journal) == 0) {
 160                                /* We were able to recover space; yay! */
 161                                ;
 162                        } else if (tid) {
 163                                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\n", __func__);
 170                                WARN_ON(1);
 171                                journal_abort(journal, 0);
 172                        }
 173                        spin_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/*
 182 * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 183 * The caller must restart a list walk.  Wait for someone else to run
 184 * jbd_unlock_bh_state().
 185 */
 186static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
 187        __releases(journal->j_list_lock)
 188{
 189        get_bh(bh);
 190        spin_unlock(&journal->j_list_lock);
 191        jbd_lock_bh_state(bh);
 192        jbd_unlock_bh_state(bh);
 193        put_bh(bh);
 194}
 195
 196/*
 197 * Clean up transaction's list of buffers submitted for io.
 198 * We wait for any pending IO to complete and remove any clean
 199 * buffers. Note that we take the buffers in the opposite ordering
 200 * from the one in which they were submitted for IO.
 201 *
 202 * Return 0 on success, and return <0 if some buffers have failed
 203 * to be written out.
 204 *
 205 * Called with j_list_lock held.
 206 */
 207static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
 208{
 209        struct journal_head *jh;
 210        struct buffer_head *bh;
 211        tid_t this_tid;
 212        int released = 0;
 213        int ret = 0;
 214
 215        this_tid = transaction->t_tid;
 216restart:
 217        /* Did somebody clean up the transaction in the meanwhile? */
 218        if (journal->j_checkpoint_transactions != transaction ||
 219                        transaction->t_tid != this_tid)
 220                return ret;
 221        while (!released && transaction->t_checkpoint_io_list) {
 222                jh = transaction->t_checkpoint_io_list;
 223                bh = jh2bh(jh);
 224                if (!jbd_trylock_bh_state(bh)) {
 225                        jbd_sync_bh(journal, bh);
 226                        spin_lock(&journal->j_list_lock);
 227                        goto restart;
 228                }
 229                get_bh(bh);
 230                if (buffer_locked(bh)) {
 231                        spin_unlock(&journal->j_list_lock);
 232                        jbd_unlock_bh_state(bh);
 233                        wait_on_buffer(bh);
 234                        /* the journal_head may have gone by now */
 235                        BUFFER_TRACE(bh, "brelse");
 236                        __brelse(bh);
 237                        spin_lock(&journal->j_list_lock);
 238                        goto restart;
 239                }
 240                if (unlikely(buffer_write_io_error(bh)))
 241                        ret = -EIO;
 242
 243                /*
 244                 * Now in whatever state the buffer currently is, we know that
 245                 * it has been written out and so we can drop it from the list
 246                 */
 247                released = __journal_remove_checkpoint(jh);
 248                jbd_unlock_bh_state(bh);
 249                __brelse(bh);
 250        }
 251
 252        return ret;
 253}
 254
 255#define NR_BATCH        64
 256
 257static void
 258__flush_batch(journal_t *journal, struct buffer_head **bhs, int *batch_count)
 259{
 260        int i;
 261        struct blk_plug plug;
 262
 263        blk_start_plug(&plug);
 264        for (i = 0; i < *batch_count; i++)
 265                write_dirty_buffer(bhs[i], WRITE_SYNC);
 266        blk_finish_plug(&plug);
 267
 268        for (i = 0; i < *batch_count; i++) {
 269                struct buffer_head *bh = bhs[i];
 270                clear_buffer_jwrite(bh);
 271                BUFFER_TRACE(bh, "brelse");
 272                __brelse(bh);
 273        }
 274        *batch_count = 0;
 275}
 276
 277/*
 278 * Try to flush one buffer from the checkpoint list to disk.
 279 *
 280 * Return 1 if something happened which requires us to abort the current
 281 * scan of the checkpoint list.  Return <0 if the buffer has failed to
 282 * be written out.
 283 *
 284 * Called with j_list_lock held and drops it if 1 is returned
 285 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 286 */
 287static int __process_buffer(journal_t *journal, struct journal_head *jh,
 288                        struct buffer_head **bhs, int *batch_count)
 289{
 290        struct buffer_head *bh = jh2bh(jh);
 291        int ret = 0;
 292
 293        if (buffer_locked(bh)) {
 294                get_bh(bh);
 295                spin_unlock(&journal->j_list_lock);
 296                jbd_unlock_bh_state(bh);
 297                wait_on_buffer(bh);
 298                /* the journal_head may have gone by now */
 299                BUFFER_TRACE(bh, "brelse");
 300                __brelse(bh);
 301                ret = 1;
 302        } else if (jh->b_transaction != NULL) {
 303                transaction_t *t = jh->b_transaction;
 304                tid_t tid = t->t_tid;
 305
 306                spin_unlock(&journal->j_list_lock);
 307                jbd_unlock_bh_state(bh);
 308                log_start_commit(journal, tid);
 309                log_wait_commit(journal, tid);
 310                ret = 1;
 311        } else if (!buffer_dirty(bh)) {
 312                ret = 1;
 313                if (unlikely(buffer_write_io_error(bh)))
 314                        ret = -EIO;
 315                get_bh(bh);
 316                J_ASSERT_JH(jh, !buffer_jbddirty(bh));
 317                BUFFER_TRACE(bh, "remove from checkpoint");
 318                __journal_remove_checkpoint(jh);
 319                spin_unlock(&journal->j_list_lock);
 320                jbd_unlock_bh_state(bh);
 321                __brelse(bh);
 322        } else {
 323                /*
 324                 * Important: we are about to write the buffer, and
 325                 * possibly block, while still holding the journal lock.
 326                 * We cannot afford to let the transaction logic start
 327                 * messing around with this buffer before we write it to
 328                 * disk, as that would break recoverability.
 329                 */
 330                BUFFER_TRACE(bh, "queue");
 331                get_bh(bh);
 332                J_ASSERT_BH(bh, !buffer_jwrite(bh));
 333                set_buffer_jwrite(bh);
 334                bhs[*batch_count] = bh;
 335                __buffer_relink_io(jh);
 336                jbd_unlock_bh_state(bh);
 337                (*batch_count)++;
 338                if (*batch_count == NR_BATCH) {
 339                        spin_unlock(&journal->j_list_lock);
 340                        __flush_batch(journal, bhs, batch_count);
 341                        ret = 1;
 342                }
 343        }
 344        return ret;
 345}
 346
 347/*
 348 * Perform an actual checkpoint. We take the first transaction on the
 349 * list of transactions to be checkpointed and send all its buffers
 350 * to disk. We submit larger chunks of data at once.
 351 *
 352 * The journal should be locked before calling this function.
 353 * Called with j_checkpoint_mutex held.
 354 */
 355int log_do_checkpoint(journal_t *journal)
 356{
 357        transaction_t *transaction;
 358        tid_t this_tid;
 359        int result;
 360
 361        jbd_debug(1, "Start checkpoint\n");
 362
 363        /*
 364         * First thing: if there are any transactions in the log which
 365         * don't need checkpointing, just eliminate them from the
 366         * journal straight away.
 367         */
 368        result = cleanup_journal_tail(journal);
 369        trace_jbd_checkpoint(journal, result);
 370        jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
 371        if (result <= 0)
 372                return result;
 373
 374        /*
 375         * OK, we need to start writing disk blocks.  Take one transaction
 376         * and write it.
 377         */
 378        result = 0;
 379        spin_lock(&journal->j_list_lock);
 380        if (!journal->j_checkpoint_transactions)
 381                goto out;
 382        transaction = journal->j_checkpoint_transactions;
 383        this_tid = transaction->t_tid;
 384restart:
 385        /*
 386         * If someone cleaned up this transaction while we slept, we're
 387         * done (maybe it's a new transaction, but it fell at the same
 388         * address).
 389         */
 390        if (journal->j_checkpoint_transactions == transaction &&
 391                        transaction->t_tid == this_tid) {
 392                int batch_count = 0;
 393                struct buffer_head *bhs[NR_BATCH];
 394                struct journal_head *jh;
 395                int retry = 0, err;
 396
 397                while (!retry && transaction->t_checkpoint_list) {
 398                        struct buffer_head *bh;
 399
 400                        jh = transaction->t_checkpoint_list;
 401                        bh = jh2bh(jh);
 402                        if (!jbd_trylock_bh_state(bh)) {
 403                                jbd_sync_bh(journal, bh);
 404                                retry = 1;
 405                                break;
 406                        }
 407                        retry = __process_buffer(journal, jh, bhs,&batch_count);
 408                        if (retry < 0 && !result)
 409                                result = retry;
 410                        if (!retry && (need_resched() ||
 411                                spin_needbreak(&journal->j_list_lock))) {
 412                                spin_unlock(&journal->j_list_lock);
 413                                retry = 1;
 414                                break;
 415                        }
 416                }
 417
 418                if (batch_count) {
 419                        if (!retry) {
 420                                spin_unlock(&journal->j_list_lock);
 421                                retry = 1;
 422                        }
 423                        __flush_batch(journal, bhs, &batch_count);
 424                }
 425
 426                if (retry) {
 427                        spin_lock(&journal->j_list_lock);
 428                        goto restart;
 429                }
 430                /*
 431                 * Now we have cleaned up the first transaction's checkpoint
 432                 * list. Let's clean up the second one
 433                 */
 434                err = __wait_cp_io(journal, transaction);
 435                if (!result)
 436                        result = err;
 437        }
 438out:
 439        spin_unlock(&journal->j_list_lock);
 440        if (result < 0)
 441                journal_abort(journal, result);
 442        else
 443                result = cleanup_journal_tail(journal);
 444
 445        return (result < 0) ? result : 0;
 446}
 447
 448/*
 449 * Check the list of checkpoint transactions for the journal to see if
 450 * we have already got rid of any since the last update of the log tail
 451 * in the journal superblock.  If so, we can instantly roll the
 452 * superblock forward to remove those transactions from the log.
 453 *
 454 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 455 *
 456 * This is the only part of the journaling code which really needs to be
 457 * aware of transaction aborts.  Checkpointing involves writing to the
 458 * main filesystem area rather than to the journal, so it can proceed
 459 * even in abort state, but we must not update the super block if
 460 * checkpointing may have failed.  Otherwise, we would lose some metadata
 461 * buffers which should be written-back to the filesystem.
 462 */
 463
 464int cleanup_journal_tail(journal_t *journal)
 465{
 466        transaction_t * transaction;
 467        tid_t           first_tid;
 468        unsigned int    blocknr, freed;
 469
 470        if (is_journal_aborted(journal))
 471                return 1;
 472
 473        /*
 474         * OK, work out the oldest transaction remaining in the log, and
 475         * the log block it starts at.
 476         *
 477         * If the log is now empty, we need to work out which is the
 478         * next transaction ID we will write, and where it will
 479         * start.
 480         */
 481        spin_lock(&journal->j_state_lock);
 482        spin_lock(&journal->j_list_lock);
 483        transaction = journal->j_checkpoint_transactions;
 484        if (transaction) {
 485                first_tid = transaction->t_tid;
 486                blocknr = transaction->t_log_start;
 487        } else if ((transaction = journal->j_committing_transaction) != NULL) {
 488                first_tid = transaction->t_tid;
 489                blocknr = transaction->t_log_start;
 490        } else if ((transaction = journal->j_running_transaction) != NULL) {
 491                first_tid = transaction->t_tid;
 492                blocknr = journal->j_head;
 493        } else {
 494                first_tid = journal->j_transaction_sequence;
 495                blocknr = journal->j_head;
 496        }
 497        spin_unlock(&journal->j_list_lock);
 498        J_ASSERT(blocknr != 0);
 499
 500        /* If the oldest pinned transaction is at the tail of the log
 501           already then there's not much we can do right now. */
 502        if (journal->j_tail_sequence == first_tid) {
 503                spin_unlock(&journal->j_state_lock);
 504                return 1;
 505        }
 506        spin_unlock(&journal->j_state_lock);
 507
 508        /*
 509         * We need to make sure that any blocks that were recently written out
 510         * --- perhaps by log_do_checkpoint() --- are flushed out before we
 511         * drop the transactions from the journal. Similarly we need to be sure
 512         * superblock makes it to disk before next transaction starts reusing
 513         * freed space (otherwise we could replay some blocks of the new
 514         * transaction thinking they belong to the old one). So we use
 515         * WRITE_FLUSH_FUA. It's unlikely this will be necessary, especially
 516         * with an appropriately sized journal, but we need this to guarantee
 517         * correctness.  Fortunately cleanup_journal_tail() doesn't get called
 518         * all that often.
 519         */
 520        journal_update_sb_log_tail(journal, first_tid, blocknr,
 521                                   WRITE_FLUSH_FUA);
 522
 523        spin_lock(&journal->j_state_lock);
 524        /* OK, update the superblock to recover the freed space.
 525         * Physical blocks come first: have we wrapped beyond the end of
 526         * the log?  */
 527        freed = blocknr - journal->j_tail;
 528        if (blocknr < journal->j_tail)
 529                freed = freed + journal->j_last - journal->j_first;
 530
 531        trace_jbd_cleanup_journal_tail(journal, first_tid, blocknr, freed);
 532        jbd_debug(1,
 533                  "Cleaning journal tail from %d to %d (offset %u), "
 534                  "freeing %u\n",
 535                  journal->j_tail_sequence, first_tid, blocknr, freed);
 536
 537        journal->j_free += freed;
 538        journal->j_tail_sequence = first_tid;
 539        journal->j_tail = blocknr;
 540        spin_unlock(&journal->j_state_lock);
 541        return 0;
 542}
 543
 544
 545/* Checkpoint list management */
 546
 547/*
 548 * journal_clean_one_cp_list
 549 *
 550 * Find all the written-back checkpoint buffers in the given list and release
 551 * them.
 552 *
 553 * Called with j_list_lock held.
 554 * Returns number of buffers reaped (for debug)
 555 */
 556
 557static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
 558{
 559        struct journal_head *last_jh;
 560        struct journal_head *next_jh = jh;
 561        int ret, freed = 0;
 562
 563        *released = 0;
 564        if (!jh)
 565                return 0;
 566
 567        last_jh = jh->b_cpprev;
 568        do {
 569                jh = next_jh;
 570                next_jh = jh->b_cpnext;
 571                /* Use trylock because of the ranking */
 572                if (jbd_trylock_bh_state(jh2bh(jh))) {
 573                        ret = __try_to_free_cp_buf(jh);
 574                        if (ret) {
 575                                freed++;
 576                                if (ret == 2) {
 577                                        *released = 1;
 578                                        return freed;
 579                                }
 580                        }
 581                }
 582                /*
 583                 * This function only frees up some memory
 584                 * if possible so we dont have an obligation
 585                 * to finish processing. Bail out if preemption
 586                 * requested:
 587                 */
 588                if (need_resched())
 589                        return freed;
 590        } while (jh != last_jh);
 591
 592        return freed;
 593}
 594
 595/*
 596 * journal_clean_checkpoint_list
 597 *
 598 * Find all the written-back checkpoint buffers in the journal and release them.
 599 *
 600 * Called with the journal locked.
 601 * Called with j_list_lock held.
 602 * Returns number of buffers reaped (for debug)
 603 */
 604
 605int __journal_clean_checkpoint_list(journal_t *journal)
 606{
 607        transaction_t *transaction, *last_transaction, *next_transaction;
 608        int ret = 0;
 609        int released;
 610
 611        transaction = journal->j_checkpoint_transactions;
 612        if (!transaction)
 613                goto out;
 614
 615        last_transaction = transaction->t_cpprev;
 616        next_transaction = transaction;
 617        do {
 618                transaction = next_transaction;
 619                next_transaction = transaction->t_cpnext;
 620                ret += journal_clean_one_cp_list(transaction->
 621                                t_checkpoint_list, &released);
 622                /*
 623                 * This function only frees up some memory if possible so we
 624                 * dont have an obligation to finish processing. Bail out if
 625                 * preemption requested:
 626                 */
 627                if (need_resched())
 628                        goto out;
 629                if (released)
 630                        continue;
 631                /*
 632                 * It is essential that we are as careful as in the case of
 633                 * t_checkpoint_list with removing the buffer from the list as
 634                 * we can possibly see not yet submitted buffers on io_list
 635                 */
 636                ret += journal_clean_one_cp_list(transaction->
 637                                t_checkpoint_io_list, &released);
 638                if (need_resched())
 639                        goto out;
 640        } while (transaction != last_transaction);
 641out:
 642        return ret;
 643}
 644
 645/*
 646 * journal_remove_checkpoint: called after a buffer has been committed
 647 * to disk (either by being write-back flushed to disk, or being
 648 * committed to the log).
 649 *
 650 * We cannot safely clean a transaction out of the log until all of the
 651 * buffer updates committed in that transaction have safely been stored
 652 * elsewhere on disk.  To achieve this, all of the buffers in a
 653 * transaction need to be maintained on the transaction's checkpoint
 654 * lists until they have been rewritten, at which point this function is
 655 * called to remove the buffer from the existing transaction's
 656 * checkpoint lists.
 657 *
 658 * The function returns 1 if it frees the transaction, 0 otherwise.
 659 * The function can free jh and bh.
 660 *
 661 * This function is called with j_list_lock held.
 662 * This function is called with jbd_lock_bh_state(jh2bh(jh))
 663 */
 664
 665int __journal_remove_checkpoint(struct journal_head *jh)
 666{
 667        transaction_t *transaction;
 668        journal_t *journal;
 669        int ret = 0;
 670
 671        JBUFFER_TRACE(jh, "entry");
 672
 673        if ((transaction = jh->b_cp_transaction) == NULL) {
 674                JBUFFER_TRACE(jh, "not on transaction");
 675                goto out;
 676        }
 677        journal = transaction->t_journal;
 678
 679        JBUFFER_TRACE(jh, "removing from transaction");
 680        __buffer_unlink(jh);
 681        jh->b_cp_transaction = NULL;
 682        journal_put_journal_head(jh);
 683
 684        if (transaction->t_checkpoint_list != NULL ||
 685            transaction->t_checkpoint_io_list != NULL)
 686                goto out;
 687
 688        /*
 689         * There is one special case to worry about: if we have just pulled the
 690         * buffer off a running or committing transaction's checkpoing list,
 691         * then even if the checkpoint list is empty, the transaction obviously
 692         * cannot be dropped!
 693         *
 694         * The locking here around t_state is a bit sleazy.
 695         * See the comment at the end of journal_commit_transaction().
 696         */
 697        if (transaction->t_state != T_FINISHED)
 698                goto out;
 699
 700        /* OK, that was the last buffer for the transaction: we can now
 701           safely remove this transaction from the log */
 702
 703        __journal_drop_transaction(journal, transaction);
 704
 705        /* Just in case anybody was waiting for more transactions to be
 706           checkpointed... */
 707        wake_up(&journal->j_wait_logspace);
 708        ret = 1;
 709out:
 710        return ret;
 711}
 712
 713/*
 714 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 715 * list so that we know when it is safe to clean the transaction out of
 716 * the log.
 717 *
 718 * Called with the journal locked.
 719 * Called with j_list_lock held.
 720 */
 721void __journal_insert_checkpoint(struct journal_head *jh,
 722                               transaction_t *transaction)
 723{
 724        JBUFFER_TRACE(jh, "entry");
 725        J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 726        J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 727
 728        /* Get reference for checkpointing transaction */
 729        journal_grab_journal_head(jh2bh(jh));
 730        jh->b_cp_transaction = transaction;
 731
 732        if (!transaction->t_checkpoint_list) {
 733                jh->b_cpnext = jh->b_cpprev = jh;
 734        } else {
 735                jh->b_cpnext = transaction->t_checkpoint_list;
 736                jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
 737                jh->b_cpprev->b_cpnext = jh;
 738                jh->b_cpnext->b_cpprev = jh;
 739        }
 740        transaction->t_checkpoint_list = jh;
 741}
 742
 743/*
 744 * We've finished with this transaction structure: adios...
 745 *
 746 * The transaction must have no links except for the checkpoint by this
 747 * point.
 748 *
 749 * Called with the journal locked.
 750 * Called with j_list_lock held.
 751 */
 752
 753void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 754{
 755        assert_spin_locked(&journal->j_list_lock);
 756        if (transaction->t_cpnext) {
 757                transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
 758                transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
 759                if (journal->j_checkpoint_transactions == transaction)
 760                        journal->j_checkpoint_transactions =
 761                                transaction->t_cpnext;
 762                if (journal->j_checkpoint_transactions == transaction)
 763                        journal->j_checkpoint_transactions = NULL;
 764        }
 765
 766        J_ASSERT(transaction->t_state == T_FINISHED);
 767        J_ASSERT(transaction->t_buffers == NULL);
 768        J_ASSERT(transaction->t_sync_datalist == NULL);
 769        J_ASSERT(transaction->t_forget == NULL);
 770        J_ASSERT(transaction->t_iobuf_list == NULL);
 771        J_ASSERT(transaction->t_shadow_list == NULL);
 772        J_ASSERT(transaction->t_log_list == NULL);
 773        J_ASSERT(transaction->t_checkpoint_list == NULL);
 774        J_ASSERT(transaction->t_checkpoint_io_list == NULL);
 775        J_ASSERT(transaction->t_updates == 0);
 776        J_ASSERT(journal->j_committing_transaction != transaction);
 777        J_ASSERT(journal->j_running_transaction != transaction);
 778
 779        trace_jbd_drop_transaction(journal, transaction);
 780        jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
 781        kfree(transaction);
 782}
 783
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