fs/jbd/commit.c

   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         spin_lock(&journal->j_state_lock);
 474         commit_transaction->t_state = T_COMMIT;
 475         spin_unlock(&journal->j_state_lock);
 476
 477         J_ASSERT(commit_transaction->t_nr_buffers <=
 478                  commit_transaction->t_outstanding_credits);
 479
 480         descriptor = NULL;
 481         bufs = 0;
 482         while (commit_transaction->t_buffers) {
 483
 484                 /* Find the next buffer to be journaled... */
 485
 486                 jh = commit_transaction->t_buffers;
 487
 488                 /* If we're in abort mode, we just un-journal the buffer and
 489                    release it for background writing. */
 490
 491                 if (is_journal_aborted(journal)) {
 492                         JBUFFER_TRACE(jh, "journal is aborting: refile");
 493                         journal_refile_buffer(journal, jh);
 494                         /* If that was the last one, we need to clean up
 495                          * any descriptor buffers which may have been
 496                          * already allocated, even if we are now
 497                          * aborting. */
 498                         if (!commit_transaction->t_buffers)
 499                                 goto start_journal_io;
 500                         continue;
 501                 }
 502
 503                 /* Make sure we have a descriptor block in which to
 504                    record the metadata buffer. */
 505
 506                 if (!descriptor) {
 507                         struct buffer_head *bh;
 508
 509                         J_ASSERT (bufs == 0);
 510
 511                         jbd_debug(4, "JBD: get descriptor\n");
 512
 513                         descriptor = journal_get_descriptor_buffer(journal);
 514                         if (!descriptor) {
 515                                 journal_abort(journal, -EIO);
 516                                 continue;
 517                         }
 518
 519                         bh = jh2bh(descriptor);
 520                         jbd_debug(4, "JBD: got buffer %llu (%p)\n",
 521                                 (unsigned long long)bh->b_blocknr, bh->b_data);
 522                         header = (journal_header_t *)&bh->b_data[0];
 523                         header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
 524                         header->h_blocktype = cpu_to_be32(JFS_DESCRIPTOR_BLOCK);
 525                         header->h_sequence  = cpu_to_be32(commit_transaction->t_tid);
 526
 527                         tagp = &bh->b_data[sizeof(journal_header_t)];
 528                         space_left = bh->b_size - sizeof(journal_header_t);
 529                         first_tag = 1;
 530                         set_buffer_jwrite(bh);
 531                         set_buffer_dirty(bh);
 532                         wbuf[bufs++] = bh;
 533
 534                         /* Record it so that we can wait for IO
 535                            completion later */
 536                         BUFFER_TRACE(bh, "ph3: file as descriptor");
 537                         journal_file_buffer(descriptor, commit_transaction,
 538                                         BJ_LogCtl);
 539                 }
 540
 541                 /* Where is the buffer to be written? */
 542
 543                 err = journal_next_log_block(journal, &blocknr);
 544                 /* If the block mapping failed, just abandon the buffer
 545                    and repeat this loop: we'll fall into the
 546                    refile-on-abort condition above. */
 547                 if (err) {
 548                         journal_abort(journal, err);
 549                         continue;
 550                 }
 551
 552                 /*
 553                  * start_this_handle() uses t_outstanding_credits to determine
 554                  * the free space in the log, but this counter is changed
 555                  * by journal_next_log_block() also.
 556                  */
 557                 commit_transaction->t_outstanding_credits--;
 558
 559                 /* Bump b_count to prevent truncate from stumbling over
 560                    the shadowed buffer!  @@@ This can go if we ever get
 561                    rid of the BJ_IO/BJ_Shadow pairing of buffers. */
 562                 atomic_inc(&jh2bh(jh)->b_count);
 563
 564                 /* Make a temporary IO buffer with which to write it out
 565                    (this will requeue both the metadata buffer and the
 566                    temporary IO buffer). new_bh goes on BJ_IO*/
 567
 568                 set_bit(BH_JWrite, &jh2bh(jh)->b_state);
 569                 /*
 570                  * akpm: journal_write_metadata_buffer() sets
 571                  * new_bh->b_transaction to commit_transaction.
 572                  * We need to clean this up before we release new_bh
 573                  * (which is of type BJ_IO)
 574                  */
 575                 JBUFFER_TRACE(jh, "ph3: write metadata");
 576                 flags = journal_write_metadata_buffer(commit_transaction,
 577                                                       jh, &new_jh, blocknr);
 578                 set_bit(BH_JWrite, &jh2bh(new_jh)->b_state);
 579                 wbuf[bufs++] = jh2bh(new_jh);
 580
 581                 /* Record the new block's tag in the current descriptor
 582                    buffer */
 583
 584                 tag_flag = 0;
 585                 if (flags & 1)
 586                         tag_flag |= JFS_FLAG_ESCAPE;
 587                 if (!first_tag)
 588                         tag_flag |= JFS_FLAG_SAME_UUID;
 589
 590                 tag = (journal_block_tag_t *) tagp;
 591                 tag->t_blocknr = cpu_to_be32(jh2bh(jh)->b_blocknr);
 592                 tag->t_flags = cpu_to_be32(tag_flag);
 593                 tagp += sizeof(journal_block_tag_t);
 594                 space_left -= sizeof(journal_block_tag_t);
 595
 596                 if (first_tag) {
 597                         memcpy (tagp, journal->j_uuid, 16);
 598                         tagp += 16;
 599                         space_left -= 16;
 600                         first_tag = 0;
 601                 }
 602
 603                 /* If there's no more to do, or if the descriptor is full,
 604                    let the IO rip! */
 605
 606                 if (bufs == journal->j_wbufsize ||
 607                     commit_transaction->t_buffers == NULL ||
 608                     space_left < sizeof(journal_block_tag_t) + 16) {
 609
 610                         jbd_debug(4, "JBD: Submit %d IOs\n", bufs);
 611
 612                         /* Write an end-of-descriptor marker before
 613                            submitting the IOs.  "tag" still points to
 614                            the last tag we set up. */
 615
 616                         tag->t_flags |= cpu_to_be32(JFS_FLAG_LAST_TAG);
 617
 618 start_journal_io:
 619                         for (i = 0; i < bufs; i++) {
 620                                 struct buffer_head *bh = wbuf[i];
 621                                 lock_buffer(bh);
 622                                 clear_buffer_dirty(bh);
 623                                 set_buffer_uptodate(bh);
 624                                 bh->b_end_io = journal_end_buffer_io_sync;
 625                                 submit_bh(WRITE, bh);
 626                         }
 627                         cond_resched();
 628
 629                         /* Force a new descriptor to be generated next
 630                            time round the loop. */
 631                         descriptor = NULL;
 632                         bufs = 0;
 633                 }
 634         }
 635
 636         /* Lo and behold: we have just managed to send a transaction to
 637            the log.  Before we can commit it, wait for the IO so far to
 638            complete.  Control buffers being written are on the
 639            transaction's t_log_list queue, and metadata buffers are on
 640            the t_iobuf_list queue.
 641
 642            Wait for the buffers in reverse order.  That way we are
 643            less likely to be woken up until all IOs have completed, and
 644            so we incur less scheduling load.
 645         */
 646
 647         jbd_debug(3, "JBD: commit phase 4\n");
 648
 649         /*
 650          * akpm: these are BJ_IO, and j_list_lock is not needed.
 651          * See __journal_try_to_free_buffer.
 652          */
 653 wait_for_iobuf:
 654         while (commit_transaction->t_iobuf_list != NULL) {
 655                 struct buffer_head *bh;
 656
 657                 jh = commit_transaction->t_iobuf_list->b_tprev;
 658                 bh = jh2bh(jh);
 659                 if (buffer_locked(bh)) {
 660                         wait_on_buffer(bh);
 661                         goto wait_for_iobuf;
 662                 }
 663                 if (cond_resched())
 664                         goto wait_for_iobuf;
 665
 666                 if (unlikely(!buffer_uptodate(bh)))
 667                         err = -EIO;
 668
 669                 clear_buffer_jwrite(bh);
 670
 671                 JBUFFER_TRACE(jh, "ph4: unfile after journal write");
 672                 journal_unfile_buffer(journal, jh);
 673
 674                 /*
 675                  * ->t_iobuf_list should contain only dummy buffer_heads
 676                  * which were created by journal_write_metadata_buffer().
 677                  */
 678                 BUFFER_TRACE(bh, "dumping temporary bh");
 679                 journal_put_journal_head(jh);
 680                 __brelse(bh);
 681                 J_ASSERT_BH(bh, atomic_read(&bh->b_count) == 0);
 682                 free_buffer_head(bh);
 683
 684                 /* We also have to unlock and free the corresponding
 685                    shadowed buffer */
 686                 jh = commit_transaction->t_shadow_list->b_tprev;
 687                 bh = jh2bh(jh);
 688                 clear_bit(BH_JWrite, &bh->b_state);
 689                 J_ASSERT_BH(bh, buffer_jbddirty(bh));
 690
 691                 /* The metadata is now released for reuse, but we need
 692                    to remember it against this transaction so that when
 693                    we finally commit, we can do any checkpointing
 694                    required. */
 695                 JBUFFER_TRACE(jh, "file as BJ_Forget");
 696                 journal_file_buffer(jh, commit_transaction, BJ_Forget);
 697                 /* Wake up any transactions which were waiting for this
 698                    IO to complete */
 699                 wake_up_bit(&bh->b_state, BH_Unshadow);
 700                 JBUFFER_TRACE(jh, "brelse shadowed buffer");
 701                 __brelse(bh);
 702         }
 703
 704         J_ASSERT (commit_transaction->t_shadow_list == NULL);
 705
 706         jbd_debug(3, "JBD: commit phase 5\n");
 707
 708         /* Here we wait for the revoke record and descriptor record buffers */
 709  wait_for_ctlbuf:
 710         while (commit_transaction->t_log_list != NULL) {
 711                 struct buffer_head *bh;
 712
 713                 jh = commit_transaction->t_log_list->b_tprev;
 714                 bh = jh2bh(jh);
 715                 if (buffer_locked(bh)) {
 716                         wait_on_buffer(bh);
 717                         goto wait_for_ctlbuf;
 718                 }
 719                 if (cond_resched())
 720                         goto wait_for_ctlbuf;
 721
 722                 if (unlikely(!buffer_uptodate(bh)))
 723                         err = -EIO;
 724
 725                 BUFFER_TRACE(bh, "ph5: control buffer writeout done: unfile");
 726                 clear_buffer_jwrite(bh);
 727                 journal_unfile_buffer(journal, jh);
 728                 journal_put_journal_head(jh);
 729                 __brelse(bh);           /* One for getblk */
 730                 /* AKPM: bforget here */
 731         }
 732
 733         jbd_debug(3, "JBD: commit phase 6\n");
 734
 735         if (journal_write_commit_record(journal, commit_transaction))
 736                 err = -EIO;
 737
 738         if (err)
 739                 journal_abort(journal, err);
 740
 741         /* End of a transaction!  Finally, we can do checkpoint
 742            processing: any buffers committed as a result of this
 743            transaction can be removed from any checkpoint list it was on
 744            before. */
 745
 746         jbd_debug(3, "JBD: commit phase 7\n");
 747
 748         J_ASSERT(commit_transaction->t_sync_datalist == NULL);
 749         J_ASSERT(commit_transaction->t_buffers == NULL);
 750         J_ASSERT(commit_transaction->t_checkpoint_list == NULL);
 751         J_ASSERT(commit_transaction->t_iobuf_list == NULL);
 752         J_ASSERT(commit_transaction->t_shadow_list == NULL);
 753         J_ASSERT(commit_transaction->t_log_list == NULL);
 754
 755 restart_loop:
 756         /*
 757          * As there are other places (journal_unmap_buffer()) adding buffers
 758          * to this list we have to be careful and hold the j_list_lock.
 759          */
 760         spin_lock(&journal->j_list_lock);
 761         while (commit_transaction->t_forget) {
 762                 transaction_t *cp_transaction;
 763                 struct buffer_head *bh;
 764
 765                 jh = commit_transaction->t_forget;
 766                 spin_unlock(&journal->j_list_lock);
 767                 bh = jh2bh(jh);
 768                 jbd_lock_bh_state(bh);
 769                 J_ASSERT_JH(jh, jh->b_transaction == commit_transaction ||
 770                         jh->b_transaction == journal->j_running_transaction);
 771
 772                 /*
 773                  * If there is undo-protected committed data against
 774                  * this buffer, then we can remove it now.  If it is a
 775                  * buffer needing such protection, the old frozen_data
 776                  * field now points to a committed version of the
 777                  * buffer, so rotate that field to the new committed
 778                  * data.
 779                  *
 780                  * Otherwise, we can just throw away the frozen data now.
 781                  */
 782                 if (jh->b_committed_data) {
 783                         jbd_free(jh->b_committed_data, bh->b_size);
 784                         jh->b_committed_data = NULL;
 785                         if (jh->b_frozen_data) {
 786                                 jh->b_committed_data = jh->b_frozen_data;
 787                                 jh->b_frozen_data = NULL;
 788                         }
 789                 } else if (jh->b_frozen_data) {
 790                         jbd_free(jh->b_frozen_data, bh->b_size);
 791                         jh->b_frozen_data = NULL;
 792                 }
 793
 794                 spin_lock(&journal->j_list_lock);
 795                 cp_transaction = jh->b_cp_transaction;
 796                 if (cp_transaction) {
 797                         JBUFFER_TRACE(jh, "remove from old cp transaction");
 798                         __journal_remove_checkpoint(jh);
 799                 }
 800
 801                 /* Only re-checkpoint the buffer_head if it is marked
 802                  * dirty.  If the buffer was added to the BJ_Forget list
 803                  * by journal_forget, it may no longer be dirty and
 804                  * there's no point in keeping a checkpoint record for
 805                  * it. */
 806
 807                 /* A buffer which has been freed while still being
 808                  * journaled by a previous transaction may end up still
 809                  * being dirty here, but we want to avoid writing back
 810                  * that buffer in the future now that the last use has
 811                  * been committed.  That's not only a performance gain,
 812                  * it also stops aliasing problems if the buffer is left
 813                  * behind for writeback and gets reallocated for another
 814                  * use in a different page. */
 815                 if (buffer_freed(bh)) {
 816                         clear_buffer_freed(bh);
 817                         clear_buffer_jbddirty(bh);
 818                 }
 819
 820                 if (buffer_jbddirty(bh)) {
 821                         JBUFFER_TRACE(jh, "add to new checkpointing trans");
 822                         __journal_insert_checkpoint(jh, commit_transaction);
 823                         JBUFFER_TRACE(jh, "refile for checkpoint writeback");
 824                         __journal_refile_buffer(jh);
 825                         jbd_unlock_bh_state(bh);
 826                 } else {
 827                         J_ASSERT_BH(bh, !buffer_dirty(bh));
 828                         /* The buffer on BJ_Forget list and not jbddirty means
 829                          * it has been freed by this transaction and hence it
 830                          * could not have been reallocated until this
 831                          * transaction has committed. *BUT* it could be
 832                          * reallocated once we have written all the data to
 833                          * disk and before we process the buffer on BJ_Forget
 834                          * list. */
 835                         JBUFFER_TRACE(jh, "refile or unfile freed buffer");
 836                         __journal_refile_buffer(jh);
 837                         if (!jh->b_transaction) {
 838                                 jbd_unlock_bh_state(bh);
 839                                  /* needs a brelse */
 840                                 journal_remove_journal_head(bh);
 841                                 release_buffer_page(bh);
 842                         } else
 843                                 jbd_unlock_bh_state(bh);
 844                 }
 845                 cond_resched_lock(&journal->j_list_lock);
 846         }
 847         spin_unlock(&journal->j_list_lock);
 848         /*
 849          * This is a bit sleazy.  We use j_list_lock to protect transition
 850          * of a transaction into T_FINISHED state and calling
 851          * __journal_drop_transaction(). Otherwise we could race with
 852          * other checkpointing code processing the transaction...
 853          */
 854         spin_lock(&journal->j_state_lock);
 855         spin_lock(&journal->j_list_lock);
 856         /*
 857          * Now recheck if some buffers did not get attached to the transaction
 858          * while the lock was dropped...
 859          */
 860         if (commit_transaction->t_forget) {
 861                 spin_unlock(&journal->j_list_lock);
 862                 spin_unlock(&journal->j_state_lock);
 863                 goto restart_loop;
 864         }
 865
 866         /* Done with this transaction! */
 867
 868         jbd_debug(3, "JBD: commit phase 8\n");
 869
 870         J_ASSERT(commit_transaction->t_state == T_COMMIT);
 871
 872         commit_transaction->t_state = T_FINISHED;
 873         J_ASSERT(commit_transaction == journal->j_committing_transaction);
 874         journal->j_commit_sequence = commit_transaction->t_tid;
 875         journal->j_committing_transaction = NULL;
 876         spin_unlock(&journal->j_state_lock);
 877
 878         if (commit_transaction->t_checkpoint_list == NULL &&
 879             commit_transaction->t_checkpoint_io_list == NULL) {
 880                 __journal_drop_transaction(journal, commit_transaction);
 881         } else {
 882                 if (journal->j_checkpoint_transactions == NULL) {
 883                         journal->j_checkpoint_transactions = commit_transaction;
 884                         commit_transaction->t_cpnext = commit_transaction;
 885                         commit_transaction->t_cpprev = commit_transaction;
 886                 } else {
 887                         commit_transaction->t_cpnext =
 888                                 journal->j_checkpoint_transactions;
 889                         commit_transaction->t_cpprev =
 890                                 commit_transaction->t_cpnext->t_cpprev;
 891                         commit_transaction->t_cpnext->t_cpprev =
 892                                 commit_transaction;
 893                         commit_transaction->t_cpprev->t_cpnext =
 894                                 commit_transaction;
 895                 }
 896         }
 897         spin_unlock(&journal->j_list_lock);
 898
 899         jbd_debug(1, "JBD: commit %d complete, head %d\n",
 900                   journal->j_commit_sequence, journal->j_tail_sequence);
 901
 902         wake_up(&journal->j_wait_done_commit);
 903 }