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   1 /*
   2  * linux/fs/jbd/commit.c
   3  *
   4  * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
   5  *
   6  * Copyright 1998 Red Hat corp --- 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  * Journal commit routines for the generic filesystem journaling code;
  13  * part of the ext2fs journaling system.
  14  */
  15
  16 #include <linux/time.h>
  17 #include <linux/fs.h>
  18 #include <linux/jbd.h>
  19 #include <linux/errno.h>
  20 #include <linux/slab.h>
  21 #include <linux/mm.h>
  22 #include <linux/pagemap.h>
  23
  24 /*
  25  * Default IO end handler for temporary BJ_IO buffer_heads.
  26  */
  27 static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
  28 {
  29         BUFFER_TRACE(bh, "");
  30         if (uptodate)
  31                 set_buffer_uptodate(bh);
  32         else
  33                 clear_buffer_uptodate(bh);
  34         unlock_buffer(bh);
  35 }
  36
  37 /*
  38  * When an ext3-ordered file is truncated, it is possible that many pages are
  39  * not sucessfully freed, because they are attached to a committing transaction.
  40  * After the transaction commits, these pages are left on the LRU, with no
  41  * ->mapping, and with attached buffers.  These pages are trivially reclaimable
  42  * by the VM, but their apparent absence upsets the VM accounting, and it makes
  43  * the numbers in /proc/meminfo look odd.
  44  *
  45  * So here, we have a buffer which has just come off the forget list.  Look to
  46  * see if we can strip all buffers from the backing page.
  47  *
  48  * Called under lock_journal(), and possibly under journal_datalist_lock.  The
  49  * caller provided us with a ref against the buffer, and we drop that here.
  50  */
  51 static void release_buffer_page(struct buffer_head *bh)
  52 {
  53         struct page *page;
  54
  55         if (buffer_dirty(bh))
  56                 goto nope;
  57         if (atomic_read(&bh->b_count) != 1)
  58                 goto nope;
  59         page = bh->b_page;
  60         if (!page)
  61                 goto nope;
  62         if (page->mapping)
  63                 goto nope;
  64
  65         /* OK, it's a truncated page */
  66         if (TestSetPageLocked(page))
  67                 goto nope;
  68
  69         page_cache_get(page);
  70         __brelse(bh);
  71         try_to_free_buffers(page);
  72         unlock_page(page);
  73         page_cache_release(page);
  74         return;
  75
  76 nope:
  77         __brelse(bh);
  78 }
  79
  80 /*
  81  * Try to acquire jbd_lock_bh_state() against the buffer, when j_list_lock is
  82  * held.  For ranking reasons we must trylock.  If we lose, schedule away and
  83  * return 0.  j_list_lock is dropped in this case.
  84  */
  85 static int inverted_lock(journal_t *journal, struct buffer_head *bh)
  86 {
  87         if (!jbd_trylock_bh_state(bh)) {
  88                 spin_unlock(&journal->j_list_lock);
  89                 schedule();
  90                 return 0;
  91         }
  92         return 1;
  93 }
  94
  95 /* Done it all: now write the commit record.  We should have
  96  * cleaned up our previous buffers by now, so if we are in abort
  97  * mode we can now just skip the rest of the journal write
  98  * entirely.
  99  *
 100  * Returns 1 if the journal needs to be aborted or 0 on success
 101  */
 102 static int journal_write_commit_record(journal_t *journal,
 103                                         transaction_t *commit_transaction)
 104 {
 105         struct journal_head *descriptor;
 106         struct buffer_head *bh;
 107         journal_header_t *header;
 108         int ret;
 109         int barrier_done = 0;
 110
 111         if (is_journal_aborted(journal))
 112                 return 0;
 113
 114         descriptor = journal_get_descriptor_buffer(journal);
 115         if (!descriptor)
 116                 return 1;
 117
 118         bh = jh2bh(descriptor);
 119
 120         header = (journal_header_t *)(bh->b_data);
 121         header->h_magic = cpu_to_be32(JFS_MAGIC_NUMBER);
 122         header->h_blocktype = cpu_to_be32(JFS_COMMIT_BLOCK);
 123         header->h_sequence = cpu_to_be32(commit_transaction->t_tid);
 124
 125         JBUFFER_TRACE(descriptor, "write commit block");
 126         set_buffer_dirty(bh);
 127         if (journal->j_flags & JFS_BARRIER) {
 128                 set_buffer_ordered(bh);
 129                 barrier_done = 1;
 130         }
 131         ret = sync_dirty_buffer(bh);
 132         if (barrier_done)
 133                 clear_buffer_ordered(bh);
 134         /* is it possible for another commit to fail at roughly
 135          * the same time as this one?  If so, we don't want to
 136          * trust the barrier flag in the super, but instead want
 137          * to remember if we sent a barrier request
 138          */
 139         if (ret == -EOPNOTSUPP && barrier_done) {
 140                 char b[BDEVNAME_SIZE];
 141
 142                 printk(KERN_WARNING
 143                         "JBD: barrier-based sync failed on %s - "
 144                         "disabling barriers\n",
 145                         bdevname(journal->j_dev, b));
 146                 spin_lock(&journal->j_state_lock);
 147                 journal->j_flags &= ~JFS_BARRIER;
 148                 spin_unlock(&journal->j_state_lock);
 149
 150                 /* And try again, without the barrier */
 151                 set_buffer_uptodate(bh);
 152                 set_buffer_dirty(bh);
 153                 ret = sync_dirty_buffer(bh);
 154         }
 155         put_bh(bh);             /* One for getblk() */
 156         journal_put_journal_head(descriptor);
 157
 158         return (ret == -EIO);
 159 }
 160
 161 static void journal_do_submit_data(struct buffer_head **wbuf, int bufs)
 162 {
 163         int i;
 164
 165         for (i = 0; i < bufs; i++) {
 166                 wbuf[i]->b_end_io = end_buffer_write_sync;
 167                 /* We use-up our safety reference in submit_bh() */
 168                 submit_bh(WRITE, wbuf[i]);
 169         }
 170 }
 171
 172 /*
 173  *  Submit all the data buffers to disk
 174  */
 175 static void journal_submit_data_buffers(journal_t *journal,
 176                                 transaction_t *commit_transaction)
 177 {
 178         struct journal_head *jh;
 179         struct buffer_head *bh;
 180         int locked;
 181         int bufs = 0;
 182         struct buffer_head **wbuf = journal->j_wbuf;
 183
 184         /*
 185          * Whenever we unlock the journal and sleep, things can get added
 186          * onto ->t_sync_datalist, so we have to keep looping back to
 187          * write_out_data until we *know* that the list is empty.
 188          *
 189          * Cleanup any flushed data buffers from the data list.  Even in
 190          * abort mode, we want to flush this out as soon as possible.
 191          */
 192 write_out_data:
 193         cond_resched();
 194         spin_lock(&journal->j_list_lock);
 195
 196         while (commit_transaction->t_sync_datalist) {
 197                 jh = commit_transaction->t_sync_datalist;
 198                 bh = jh2bh(jh);
 199                 locked = 0;
 200
 201                 /* Get reference just to make sure buffer does not disappear
 202                  * when we are forced to drop various locks */
 203                 get_bh(bh);
 204                 /* If the buffer is dirty, we need to submit IO and hence
 205                  * we need the buffer lock. We try to lock the buffer without
 206                  * blocking. If we fail, we need to drop j_list_lock and do
 207                  * blocking lock_buffer().
 208                  */
 209                 if (buffer_dirty(bh)) {
 210                         if (test_set_buffer_locked(bh)) {
 211                                 BUFFER_TRACE(bh, "needs blocking lock");
 212                                 spin_unlock(&journal->j_list_lock);
 213                                 /* Write out all data to prevent deadlocks */
 214                                 journal_do_submit_data(wbuf, bufs);
 215                                 bufs = 0;
 216                                 lock_buffer(bh);
 217                                 spin_lock(&journal->j_list_lock);
 218                         }
 219                         locked = 1;
 220                 }
 221                 /* We have to get bh_state lock. Again out of order, sigh. */
 222                 if (!inverted_lock(journal, bh)) {
 223                         jbd_lock_bh_state(bh);
 224                         spin_lock(&journal->j_list_lock);
 225                 }
 226                 /* Someone already cleaned up the buffer? */
 227                 if (!buffer_jbd(bh)
 228                         || jh->b_transaction != commit_transaction
 229                         || jh->b_jlist != BJ_SyncData) {
 230                         jbd_unlock_bh_state(bh);
 231                         if (locked)
 232                                 unlock_buffer(bh);
 233                         BUFFER_TRACE(bh, "already cleaned up");
 234                         put_bh(bh);
 235                         continue;
 236                 }
 237                 if (locked && test_clear_buffer_dirty(bh)) {
 238                         BUFFER_TRACE(bh, "needs writeout, adding to array");
 239                         wbuf[bufs++] = bh;
 240                         __journal_file_buffer(jh, commit_transaction,
 241                                                 BJ_Locked);
 242                         jbd_unlock_bh_state(bh);
 243                         if (bufs == journal->j_wbufsize) {
 244                                 spin_unlock(&journal->j_list_lock);
 245                                 journal_do_submit_data(wbuf, bufs);
 246                                 bufs = 0;
 247                                 goto write_out_data;
 248                         }
 249                 } else if (!locked && buffer_locked(bh)) {
 250                         __journal_file_buffer(jh, commit_transaction,
 251                                                 BJ_Locked);
 252                         jbd_unlock_bh_state(bh);
 253                         put_bh(bh);
 254                 } else {
 255                         BUFFER_TRACE(bh, "writeout complete: unfile");
 256                         __journal_unfile_buffer(jh);
 257                         jbd_unlock_bh_state(bh);
 258                         if (locked)
 259                                 unlock_buffer(bh);
 260                         journal_remove_journal_head(bh);
 261                         /* Once for our safety reference, once for
 262                          * journal_remove_journal_head() */
 263                         put_bh(bh);
 264                         put_bh(bh);
 265                 }
 266
 267                 if (need_resched() || spin_needbreak(&journal->j_list_lock)) {
 268                         spin_unlock(&journal->j_list_lock);
 269                         goto write_out_data;
 270                 }
 271         }
 272         spin_unlock(&journal->j_list_lock);
 273         journal_do_submit_data(wbuf, bufs);
 274 }
 275
 276 /*
 277  * journal_commit_transaction
 278  *
 279  * The primary function for committing a transaction to the log.  This
 280  * function is called by the journal thread to begin a complete commit.
 281  */
 282 void journal_commit_transaction(journal_t *journal)
 283 {
 284         transaction_t *commit_transaction;
 285         struct journal_head *jh, *new_jh, *descriptor;
 286         struct buffer_head **wbuf = journal->j_wbuf;
 287         int bufs;
 288         int flags;
 289         int err;
 290         unsigned long blocknr;
 291         char *tagp = NULL;
 292         journal_header_t *header;
 293         journal_block_tag_t *tag = NULL;
 294         int space_left = 0;
 295         int first_tag = 0;
 296         int tag_flag;
 297         int i;
 298
 299         /*
 300          * First job: lock down the current transaction and wait for
 301          * all outstanding updates to complete.
 302          */
 303
 304 #ifdef COMMIT_STATS
 305         spin_lock(&journal->j_list_lock);
 306         summarise_journal_usage(journal);
 307         spin_unlock(&journal->j_list_lock);
 308 #endif
 309
 310         /* Do we need to erase the effects of a prior journal_flush? */
 311         if (journal->j_flags & JFS_FLUSHED) {
 312                 jbd_debug(3, "super block updated\n");
 313                 journal_update_superblock(journal, 1);
 314         } else {
 315                 jbd_debug(3, "superblock not updated\n");
 316         }
 317
 318         J_ASSERT(journal->j_running_transaction != NULL);
 319         J_ASSERT(journal->j_committing_transaction == NULL);
 320
 321         commit_transaction = journal->j_running_transaction;
 322         J_ASSERT(commit_transaction->t_state == T_RUNNING);
 323
 324         jbd_debug(1, "JBD: starting commit of transaction %d\n",
 325                         commit_transaction->t_tid);
 326
 327         spin_lock(&journal->j_state_lock);
 328         commit_transaction->t_state = T_LOCKED;
 329
 330         spin_lock(&commit_transaction->t_handle_lock);
 331         while (commit_transaction->t_updates) {
 332                 DEFINE_WAIT(wait);
 333
 334                 prepare_to_wait(&journal->j_wait_updates, &wait,
 335                                         TASK_UNINTERRUPTIBLE);
 336                 if (commit_transaction->t_updates) {
 337                         spin_unlock(&commit_transaction->t_handle_lock);
 338                         spin_unlock(&journal->j_state_lock);
 339                         schedule();
 340                         spin_lock(&journal->j_state_lock);
 341                         spin_lock(&commit_transaction->t_handle_lock);
 342                 }
 343                 finish_wait(&journal->j_wait_updates, &wait);
 344         }
 345         spin_unlock(&commit_transaction->t_handle_lock);
 346
 347         J_ASSERT (commit_transaction->t_outstanding_credits <=
 348                         journal->j_max_transaction_buffers);
 349
 350         /*
 351          * First thing we are allowed to do is to discard any remaining
 352          * BJ_Reserved buffers.  Note, it is _not_ permissible to assume
 353          * that there are no such buffers: if a large filesystem
 354          * operation like a truncate needs to split itself over multiple
 355          * transactions, then it may try to do a journal_restart() while
 356          * there are still BJ_Reserved buffers outstanding.  These must
 357          * be released cleanly from the current transaction.
 358          *
 359          * In this case, the filesystem must still reserve write access
 360          * again before modifying the buffer in the new transaction, but
 361          * we do not require it to remember exactly which old buffers it
 362          * has reserved.  This is consistent with the existing behaviour
 363          * that multiple journal_get_write_access() calls to the same
 364          * buffer are perfectly permissable.
 365          */
 366         while (commit_transaction->t_reserved_list) {
 367                 jh = commit_transaction->t_reserved_list;
 368                 JBUFFER_TRACE(jh, "reserved, unused: refile");
 369                 /*
 370                  * A journal_get_undo_access()+journal_release_buffer() may
 371                  * leave undo-committed data.
 372                  */
 373                 if (jh->b_committed_data) {
 374                         struct buffer_head *bh = jh2bh(jh);
 375
 376                         jbd_lock_bh_state(bh);
 377                         jbd_free(jh->b_committed_data, bh->b_size);
 378                         jh->b_committed_data = NULL;
 379                         jbd_unlock_bh_state(bh);
 380                 }
 381                 journal_refile_buffer(journal, jh);
 382         }
 383
 384         /*
 385          * Now try to drop any written-back buffers from the journal's
 386          * checkpoint lists.  We do this *before* commit because it potentially
 387          * frees some memory
 388          */
 389         spin_lock(&journal->j_list_lock);
 390         __journal_clean_checkpoint_list(journal);
 391         spin_unlock(&journal->j_list_lock);
 392
 393         jbd_debug (3, "JBD: commit phase 1\n");
 394
 395         /*
 396          * Switch to a new revoke table.
 397          */
 398         journal_switch_revoke_table(journal);
 399
 400         commit_transaction->t_state = T_FLUSH;
 401         journal->j_committing_transaction = commit_transaction;
 402         journal->j_running_transaction = NULL;
 403         commit_transaction->t_log_start = journal->j_head;
 404         wake_up(&journal->j_wait_transaction_locked);
 405         spin_unlock(&journal->j_state_lock);
 406
 407         jbd_debug (3, "JBD: commit phase 2\n");
 408
 409         /*
 410          * Now start flushing things to disk, in the order they appear
 411          * on the transaction lists.  Data blocks go first.
 412          */
 413         err = 0;
 414         journal_submit_data_buffers(journal, commit_transaction);
 415
 416         /*
 417          * Wait for all previously submitted IO to complete.
 418          */
 419         spin_lock(&journal->j_list_lock);
 420         while (commit_transaction->t_locked_list) {
 421                 struct buffer_head *bh;
 422
 423                 jh = commit_transaction->t_locked_list->b_tprev;
 424                 bh = jh2bh(jh);
 425                 get_bh(bh);
 426                 if (buffer_locked(bh)) {
 427                         spin_unlock(&journal->j_list_lock);
 428                         wait_on_buffer(bh);
 429                         if (unlikely(!buffer_uptodate(bh)))
 430                                 err = -EIO;
 431                         spin_lock(&journal->j_list_lock);
 432                 }
 433                 if (!inverted_lock(journal, bh)) {
 434                         put_bh(bh);
 435                         spin_lock(&journal->j_list_lock);
 436                         continue;
 437                 }
 438                 if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
 439                         __journal_unfile_buffer(jh);
 440                         jbd_unlock_bh_state(bh);
 441                         journal_remove_journal_head(bh);
 442                         put_bh(bh);
 443                 } else {
 444                         jbd_unlock_bh_state(bh);
 445                 }
 446                 put_bh(bh);
 447                 cond_resched_lock(&journal->j_list_lock);
 448         }
 449         spin_unlock(&journal->j_list_lock);
 450
 451         if (err)
 452                 journal_abort(journal, err);
 453
 454         journal_write_revoke_records(journal, commit_transaction);
 455
 456         jbd_debug(3, "JBD: commit phase 2\n");
 457
 458         /*
 459          * If we found any dirty or locked buffers, then we should have
 460          * looped back up to the write_out_data label.  If there weren't
 461          * any then journal_clean_data_list should have wiped the list
 462          * clean by now, so check that it is in fact empty.
 463          */
 464         J_ASSERT (commit_transaction->t_sync_datalist == NULL);
 465
 466         jbd_debug (3, "JBD: commit phase 3\n");
 467
 468         /*
 469          * Way to go: we have now written out all of the data for a
 470          * transaction!  Now comes the tricky part: we need to write out
 471          * metadata.  Loop over the transaction's entire buffer list:
 472          */
 473         commit_transaction->t_state = T_COMMIT;
 474
 475         J_ASSERT(commit_transaction->t_nr_buffers <=
 476                  commit_transaction->t_outstanding_credits);
 477
 478         descriptor = NULL;
 479         bufs = 0;
 480         while (commit_transaction->t_buffers) {
 481
 482                 /* Find the next buffer to be journaled... */
 483
 484                 jh = commit_transaction->t_buffers;
 485
 486                 /* If we're in abort mode, we just un-journal the buffer and
 487                    release it for background writing. */
 488
 489                 if (is_journal_aborted(journal)) {
 490                         JBUFFER_TRACE(jh, "journal is aborting: refile");
 491                         journal_refile_buffer(journal, jh);
 492                         /* If that was the last one, we need to clean up
 493                          * any descriptor buffers which may have been
 494                          * already allocated, even if we are now
 495                          * aborting. */
 496                         if (!commit_transaction->t_buffers)
 497                                 goto start_journal_io;
 498                         continue;
 499                 }
 500
 501                 /* Make sure we have a descriptor block in which to
 502                    record the metadata buffer. */
 503
 504                 if (!descriptor) {
 505                         struct buffer_head *bh;
 506
 507                         J_ASSERT (bufs == 0);
 508
 509                         jbd_debug(4, "JBD: get descriptor\n");
 510
 511                         descriptor = journal_get_descriptor_buffer(journal);
 512                         if (!descriptor) {
 513                                 journal_abort(journal, -EIO);
 514                                 continue;
 515                         }
 516
 517                         bh = jh2bh(descriptor);
 518                         jbd_debug(4, "JBD: got buffer %llu (%p)\n",
 519                                 (unsigned long long)bh->b_blocknr, bh->b_data);
 520                         header = (journal_header_t *)&bh->b_data[0];
 521                         header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
 522                         header->h_blocktype = cpu_to_be32(JFS_DESCRIPTOR_BLOCK);
 523                         header->h_sequence  = cpu_to_be32(commit_transaction->t_tid);
 524
 525                         tagp = &bh->b_data[sizeof(journal_header_t)];
 526                         space_left = bh->b_size - sizeof(journal_header_t);
 527                         first_tag = 1;
 528                         set_buffer_jwrite(bh);
 529                         set_buffer_dirty(bh);
 530                         wbuf[bufs++] = bh;
 531
 532                         /* Record it so that we can wait for IO
 533                            completion later */
 534                         BUFFER_TRACE(bh, "ph3: file as descriptor");
 535                         journal_file_buffer(descriptor, commit_transaction,
 536                                         BJ_LogCtl);
 537                 }
 538
 539                 /* Where is the buffer to be written? */
 540
 541                 err = journal_next_log_block(journal, &blocknr);
 542                 /* If the block mapping failed, just abandon the buffer
 543                    and repeat this loop: we'll fall into the
 544                    refile-on-abort condition above. */
 545                 if (err) {
 546                         journal_abort(journal, err);
 547                         continue;
 548                 }
 549
 550                 /*
 551                  * start_this_handle() uses t_outstanding_credits to determine
 552                  * the free space in the log, but this counter is changed
 553                  * by journal_next_log_block() also.
 554                  */
 555                 commit_transaction->t_outstanding_credits--;
 556
 557                 /* Bump b_count to prevent truncate from stumbling over
 558                    the shadowed buffer!  @@@ This can go if we ever get
 559                    rid of the BJ_IO/BJ_Shadow pairing of buffers. */
 560                 atomic_inc(&jh2bh(jh)->b_count);
 561
 562                 /* Make a temporary IO buffer with which to write it out
 563                    (this will requeue both the metadata buffer and the
 564                    temporary IO buffer). new_bh goes on BJ_IO*/
 565
 566                 set_bit(BH_JWrite, &jh2bh(jh)->b_state);
 567                 /*
 568                  * akpm: journal_write_metadata_buffer() sets
 569                  * new_bh->b_transaction to commit_transaction.
 570                  * We need to clean this up before we release new_bh
 571                  * (which is of type BJ_IO)
 572                  */
 573                 JBUFFER_TRACE(jh, "ph3: write metadata");
 574                 flags = journal_write_metadata_buffer(commit_transaction,
 575                                                       jh, &new_jh, blocknr);
 576                 set_bit(BH_JWrite, &jh2bh(new_jh)->b_state);
 577                 wbuf[bufs++] = jh2bh(new_jh);
 578
 579                 /* Record the new block's tag in the current descriptor
 580                    buffer */
 581
 582                 tag_flag = 0;
 583                 if (flags & 1)
 584                         tag_flag |= JFS_FLAG_ESCAPE;
 585                 if (!first_tag)
 586                         tag_flag |= JFS_FLAG_SAME_UUID;
 587
 588                 tag = (journal_block_tag_t *) tagp;
 589                 tag->t_blocknr = cpu_to_be32(jh2bh(jh)->b_blocknr);
 590                 tag->t_flags = cpu_to_be32(tag_flag);
 591                 tagp += sizeof(journal_block_tag_t);
 592                 space_left -= sizeof(journal_block_tag_t);
 593
 594                 if (first_tag) {
 595                         memcpy (tagp, journal->j_uuid, 16);
 596                         tagp += 16;
 597                         space_left -= 16;
 598                         first_tag = 0;
 599                 }
 600
 601                 /* If there's no more to do, or if the descriptor is full,
 602                    let the IO rip! */
 603
 604                 if (bufs == journal->j_wbufsize ||
 605                     commit_transaction->t_buffers == NULL ||
 606                     space_left < sizeof(journal_block_tag_t) + 16) {
 607
 608                         jbd_debug(4, "JBD: Submit %d IOs\n", bufs);
 609
 610                         /* Write an end-of-descriptor marker before
 611                            submitting the IOs.  "tag" still points to
 612                            the last tag we set up. */
 613
 614                         tag->t_flags |= cpu_to_be32(JFS_FLAG_LAST_TAG);
 615
 616 start_journal_io:
 617                         for (i = 0; i < bufs; i++) {
 618                                 struct buffer_head *bh = wbuf[i];
 619                                 lock_buffer(bh);
 620                                 clear_buffer_dirty(bh);
 621                                 set_buffer_uptodate(bh);
 622                                 bh->b_end_io = journal_end_buffer_io_sync;
 623                                 submit_bh(WRITE, bh);
 624                         }
 625                         cond_resched();
 626
 627                         /* Force a new descriptor to be generated next
 628                            time round the loop. */
 629                         descriptor = NULL;
 630                         bufs = 0;
 631                 }
 632         }
 633
 634         /* Lo and behold: we have just managed to send a transaction to
 635            the log.  Before we can commit it, wait for the IO so far to
 636            complete.  Control buffers being written are on the
 637            transaction's t_log_list queue, and metadata buffers are on
 638            the t_iobuf_list queue.
 639
 640            Wait for the buffers in reverse order.  That way we are
 641            less likely to be woken up until all IOs have completed, and
 642            so we incur less scheduling load.
 643         */
 644
 645         jbd_debug(3, "JBD: commit phase 4\n");
 646
 647         /*
 648          * akpm: these are BJ_IO, and j_list_lock is not needed.
 649          * See __journal_try_to_free_buffer.
 650          */
 651 wait_for_iobuf:
 652         while (commit_transaction->t_iobuf_list != NULL) {
 653                 struct buffer_head *bh;
 654
 655                 jh = commit_transaction->t_iobuf_list->b_tprev;
 656                 bh = jh2bh(jh);
 657                 if (buffer_locked(bh)) {
 658                         wait_on_buffer(bh);
 659                         goto wait_for_iobuf;
 660                 }
 661                 if (cond_resched())
 662                         goto wait_for_iobuf;
 663
 664                 if (unlikely(!buffer_uptodate(bh)))
 665                         err = -EIO;
 666
 667                 clear_buffer_jwrite(bh);
 668
 669                 JBUFFER_TRACE(jh, "ph4: unfile after journal write");
 670                 journal_unfile_buffer(journal, jh);
 671
 672                 /*
 673                  * ->t_iobuf_list should contain only dummy buffer_heads
 674                  * which were created by journal_write_metadata_buffer().
 675                  */
 676                 BUFFER_TRACE(bh, "dumping temporary bh");
 677                 journal_put_journal_head(jh);
 678                 __brelse(bh);
 679                 J_ASSERT_BH(bh, atomic_read(&bh->b_count) == 0);
 680                 free_buffer_head(bh);
 681
 682                 /* We also have to unlock and free the corresponding
 683                    shadowed buffer */
 684                 jh = commit_transaction->t_shadow_list->b_tprev;
 685                 bh = jh2bh(jh);
 686                 clear_bit(BH_JWrite, &bh->b_state);
 687                 J_ASSERT_BH(bh, buffer_jbddirty(bh));
 688
 689                 /* The metadata is now released for reuse, but we need
 690                    to remember it against this transaction so that when
 691                    we finally commit, we can do any checkpointing
 692                    required. */
 693                 JBUFFER_TRACE(jh, "file as BJ_Forget");
 694                 journal_file_buffer(jh, commit_transaction, BJ_Forget);
 695                 /* Wake up any transactions which were waiting for this
 696                    IO to complete */
 697                 wake_up_bit(&bh->b_state, BH_Unshadow);
 698                 JBUFFER_TRACE(jh, "brelse shadowed buffer");
 699                 __brelse(bh);
 700         }
 701
 702         J_ASSERT (commit_transaction->t_shadow_list == NULL);
 703
 704         jbd_debug(3, "JBD: commit phase 5\n");
 705
 706         /* Here we wait for the revoke record and descriptor record buffers */
 707  wait_for_ctlbuf:
 708         while (commit_transaction->t_log_list != NULL) {
 709                 struct buffer_head *bh;
 710
 711                 jh = commit_transaction->t_log_list->b_tprev;
 712                 bh = jh2bh(jh);
 713                 if (buffer_locked(bh)) {
 714                         wait_on_buffer(bh);
 715                         goto wait_for_ctlbuf;
 716                 }
 717                 if (cond_resched())
 718                         goto wait_for_ctlbuf;
 719
 720                 if (unlikely(!buffer_uptodate(bh)))
 721                         err = -EIO;
 722
 723                 BUFFER_TRACE(bh, "ph5: control buffer writeout done: unfile");
 724                 clear_buffer_jwrite(bh);
 725                 journal_unfile_buffer(journal, jh);
 726                 journal_put_journal_head(jh);
 727                 __brelse(bh);           /* One for getblk */
 728                 /* AKPM: bforget here */
 729         }
 730
 731         jbd_debug(3, "JBD: commit phase 6\n");
 732
 733         if (journal_write_commit_record(journal, commit_transaction))
 734                 err = -EIO;
 735
 736         if (err)
 737                 journal_abort(journal, err);
 738
 739         /* End of a transaction!  Finally, we can do checkpoint
 740            processing: any buffers committed as a result of this
 741            transaction can be removed from any checkpoint list it was on
 742            before. */
 743
 744         jbd_debug(3, "JBD: commit phase 7\n");
 745
 746         J_ASSERT(commit_transaction->t_sync_datalist == NULL);
 747         J_ASSERT(commit_transaction->t_buffers == NULL);
 748         J_ASSERT(commit_transaction->t_checkpoint_list == NULL);
 749         J_ASSERT(commit_transaction->t_iobuf_list == NULL);
 750         J_ASSERT(commit_transaction->t_shadow_list == NULL);
 751         J_ASSERT(commit_transaction->t_log_list == NULL);
 752
 753 restart_loop:
 754         /*
 755          * As there are other places (journal_unmap_buffer()) adding buffers
 756          * to this list we have to be careful and hold the j_list_lock.
 757          */
 758         spin_lock(&journal->j_list_lock);
 759         while (commit_transaction->t_forget) {
 760                 transaction_t *cp_transaction;
 761                 struct buffer_head *bh;
 762
 763                 jh = commit_transaction->t_forget;
 764                 spin_unlock(&journal->j_list_lock);
 765                 bh = jh2bh(jh);
 766                 jbd_lock_bh_state(bh);
 767                 J_ASSERT_JH(jh, jh->b_transaction == commit_transaction ||
 768                         jh->b_transaction == journal->j_running_transaction);
 769
 770                 /*
 771                  * If there is undo-protected committed data against
 772                  * this buffer, then we can remove it now.  If it is a
 773                  * buffer needing such protection, the old frozen_data
 774                  * field now points to a committed version of the
 775                  * buffer, so rotate that field to the new committed
 776                  * data.
 777                  *
 778                  * Otherwise, we can just throw away the frozen data now.
 779                  */
 780                 if (jh->b_committed_data) {
 781                         jbd_free(jh->b_committed_data, bh->b_size);
 782                         jh->b_committed_data = NULL;
 783                         if (jh->b_frozen_data) {
 784                                 jh->b_committed_data = jh->b_frozen_data;
 785                                 jh->b_frozen_data = NULL;
 786                         }
 787                 } else if (jh->b_frozen_data) {
 788                         jbd_free(jh->b_frozen_data, bh->b_size);
 789                         jh->b_frozen_data = NULL;
 790                 }
 791
 792                 spin_lock(&journal->j_list_lock);
 793                 cp_transaction = jh->b_cp_transaction;
 794                 if (cp_transaction) {
 795                         JBUFFER_TRACE(jh, "remove from old cp transaction");
 796                         __journal_remove_checkpoint(jh);
 797                 }
 798
 799                 /* Only re-checkpoint the buffer_head if it is marked
 800                  * dirty.  If the buffer was added to the BJ_Forget list
 801                  * by journal_forget, it may no longer be dirty and
 802                  * there's no point in keeping a checkpoint record for
 803                  * it. */
 804
 805                 /* A buffer which has been freed while still being
 806                  * journaled by a previous transaction may end up still
 807                  * being dirty here, but we want to avoid writing back
 808                  * that buffer in the future now that the last use has
 809                  * been committed.  That's not only a performance gain,
 810                  * it also stops aliasing problems if the buffer is left
 811                  * behind for writeback and gets reallocated for another
 812                  * use in a different page. */
 813                 if (buffer_freed(bh)) {
 814                         clear_buffer_freed(bh);
 815                         clear_buffer_jbddirty(bh);
 816                 }
 817
 818                 if (buffer_jbddirty(bh)) {
 819                         JBUFFER_TRACE(jh, "add to new checkpointing trans");
 820                         __journal_insert_checkpoint(jh, commit_transaction);
 821                         JBUFFER_TRACE(jh, "refile for checkpoint writeback");
 822                         __journal_refile_buffer(jh);
 823                         jbd_unlock_bh_state(bh);
 824                 } else {
 825                         J_ASSERT_BH(bh, !buffer_dirty(bh));
 826                         /* The buffer on BJ_Forget list and not jbddirty means
 827                          * it has been freed by this transaction and hence it
 828                          * could not have been reallocated until this
 829                          * transaction has committed. *BUT* it could be
 830                          * reallocated once we have written all the data to
 831                          * disk and before we process the buffer on BJ_Forget
 832                          * list. */
 833                         JBUFFER_TRACE(jh, "refile or unfile freed buffer");
 834                         __journal_refile_buffer(jh);
 835                         if (!jh->b_transaction) {
 836                                 jbd_unlock_bh_state(bh);
 837                                  /* needs a brelse */
 838                                 journal_remove_journal_head(bh);
 839                                 release_buffer_page(bh);
 840                         } else
 841                                 jbd_unlock_bh_state(bh);
 842                 }
 843                 cond_resched_lock(&journal->j_list_lock);
 844         }
 845         spin_unlock(&journal->j_list_lock);
 846         /*
 847          * This is a bit sleazy.  We use j_list_lock to protect transition
 848          * of a transaction into T_FINISHED state and calling
 849          * __journal_drop_transaction(). Otherwise we could race with
 850          * other checkpointing code processing the transaction...
 851          */
 852         spin_lock(&journal->j_state_lock);
 853         spin_lock(&journal->j_list_lock);
 854         /*
 855          * Now recheck if some buffers did not get attached to the transaction
 856          * while the lock was dropped...
 857          */
 858         if (commit_transaction->t_forget) {
 859                 spin_unlock(&journal->j_list_lock);
 860                 spin_unlock(&journal->j_state_lock);
 861                 goto restart_loop;
 862         }
 863
 864         /* Done with this transaction! */
 865
 866         jbd_debug(3, "JBD: commit phase 8\n");
 867
 868         J_ASSERT(commit_transaction->t_state == T_COMMIT);
 869
 870         commit_transaction->t_state = T_FINISHED;
 871         J_ASSERT(commit_transaction == journal->j_committing_transaction);
 872         journal->j_commit_sequence = commit_transaction->t_tid;
 873         journal->j_committing_transaction = NULL;
 874         spin_unlock(&journal->j_state_lock);
 875
 876         if (commit_transaction->t_checkpoint_list == NULL &&
 877             commit_transaction->t_checkpoint_io_list == NULL) {
 878                 __journal_drop_transaction(journal, commit_transaction);
 879         } else {
 880                 if (journal->j_checkpoint_transactions == NULL) {
 881                         journal->j_checkpoint_transactions = commit_transaction;
 882                         commit_transaction->t_cpnext = commit_transaction;
 883                         commit_transaction->t_cpprev = commit_transaction;
 884                 } else {
 885                         commit_transaction->t_cpnext =
 886                                 journal->j_checkpoint_transactions;
 887                         commit_transaction->t_cpprev =
 888                                 commit_transaction->t_cpnext->t_cpprev;
 889                         commit_transaction->t_cpnext->t_cpprev =
 890                                 commit_transaction;
 891                         commit_transaction->t_cpprev->t_cpnext =
 892                                 commit_transaction;
 893                 }
 894         }
 895         spin_unlock(&journal->j_list_lock);
 896
 897         jbd_debug(1, "JBD: commit %d complete, head %d\n",
 898                   journal->j_commit_sequence, journal->j_tail_sequence);
 899
 900         wake_up(&journal->j_wait_done_commit);
 901 }