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   1 /*
   2  * linux/fs/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
  26 /*
  27  * Unlink a buffer from a transaction.
  28  *
  29  * Called with j_list_lock held.
  30  */
  31
  32 static inline void __buffer_unlink(struct journal_head *jh)
  33 {
  34         transaction_t *transaction;
  35
  36         transaction = jh->b_cp_transaction;
  37         jh->b_cp_transaction = NULL;
  38
  39         jh->b_cpnext->b_cpprev = jh->b_cpprev;
  40         jh->b_cpprev->b_cpnext = jh->b_cpnext;
  41         if (transaction->t_checkpoint_list == jh)
  42                 transaction->t_checkpoint_list = jh->b_cpnext;
  43         if (transaction->t_checkpoint_list == jh)
  44                 transaction->t_checkpoint_list = NULL;
  45 }
  46
  47 /*
  48  * Try to release a checkpointed buffer from its transaction.
  49  * Returns 1 if we released it.
  50  * Requires j_list_lock
  51  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
  52  */
  53 static int __try_to_free_cp_buf(struct journal_head *jh)
  54 {
  55         int ret = 0;
  56         struct buffer_head *bh = jh2bh(jh);
  57
  58         if (jh->b_jlist == BJ_None && !buffer_locked(bh) && !buffer_dirty(bh)) {
  59                 JBUFFER_TRACE(jh, "remove from checkpoint list");
  60                 __journal_remove_checkpoint(jh);
  61                 jbd_unlock_bh_state(bh);
  62                 journal_remove_journal_head(bh);
  63                 BUFFER_TRACE(bh, "release");
  64                 __brelse(bh);
  65                 ret = 1;
  66         } else {
  67                 jbd_unlock_bh_state(bh);
  68         }
  69         return ret;
  70 }
  71
  72 /*
  73  * __log_wait_for_space: wait until there is space in the journal.
  74  *
  75  * Called under j-state_lock *only*.  It will be unlocked if we have to wait
  76  * for a checkpoint to free up some space in the log.
  77  */
  78 void __log_wait_for_space(journal_t *journal)
  79 {
  80         int nblocks;
  81         assert_spin_locked(&journal->j_state_lock);
  82
  83         nblocks = jbd_space_needed(journal);
  84         while (__log_space_left(journal) < nblocks) {
  85                 if (journal->j_flags & JFS_ABORT)
  86                         return;
  87                 spin_unlock(&journal->j_state_lock);
  88                 down(&journal->j_checkpoint_sem);
  89
  90                 /*
  91                  * Test again, another process may have checkpointed while we
  92                  * were waiting for the checkpoint lock
  93                  */
  94                 spin_lock(&journal->j_state_lock);
  95                 nblocks = jbd_space_needed(journal);
  96                 if (__log_space_left(journal) < nblocks) {
  97                         spin_unlock(&journal->j_state_lock);
  98                         log_do_checkpoint(journal);
  99                         spin_lock(&journal->j_state_lock);
 100                 }
 101                 up(&journal->j_checkpoint_sem);
 102         }
 103 }
 104
 105 /*
 106  * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 107  * The caller must restart a list walk.  Wait for someone else to run
 108  * jbd_unlock_bh_state().
 109  */
 110 static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
 111 {
 112         get_bh(bh);
 113         spin_unlock(&journal->j_list_lock);
 114         jbd_lock_bh_state(bh);
 115         jbd_unlock_bh_state(bh);
 116         put_bh(bh);
 117 }
 118
 119 /*
 120  * Clean up a transaction's checkpoint list.
 121  *
 122  * We wait for any pending IO to complete and make sure any clean
 123  * buffers are removed from the transaction.
 124  *
 125  * Return 1 if we performed any actions which might have destroyed the
 126  * checkpoint.  (journal_remove_checkpoint() deletes the transaction when
 127  * the last checkpoint buffer is cleansed)
 128  *
 129  * Called with j_list_lock held.
 130  */
 131 static int __cleanup_transaction(journal_t *journal, transaction_t *transaction)
 132 {
 133         struct journal_head *jh, *next_jh, *last_jh;
 134         struct buffer_head *bh;
 135         int ret = 0;
 136
 137         assert_spin_locked(&journal->j_list_lock);
 138         jh = transaction->t_checkpoint_list;
 139         if (!jh)
 140                 return 0;
 141
 142         last_jh = jh->b_cpprev;
 143         next_jh = jh;
 144         do {
 145                 jh = next_jh;
 146                 bh = jh2bh(jh);
 147                 if (buffer_locked(bh)) {
 148                         atomic_inc(&bh->b_count);
 149                         spin_unlock(&journal->j_list_lock);
 150                         wait_on_buffer(bh);
 151                         /* the journal_head may have gone by now */
 152                         BUFFER_TRACE(bh, "brelse");
 153                         __brelse(bh);
 154                         goto out_return_1;
 155                 }
 156
 157                 /*
 158                  * This is foul
 159                  */
 160                 if (!jbd_trylock_bh_state(bh)) {
 161                         jbd_sync_bh(journal, bh);
 162                         goto out_return_1;
 163                 }
 164
 165                 if (jh->b_transaction != NULL) {
 166                         transaction_t *t = jh->b_transaction;
 167                         tid_t tid = t->t_tid;
 168
 169                         spin_unlock(&journal->j_list_lock);
 170                         jbd_unlock_bh_state(bh);
 171                         log_start_commit(journal, tid);
 172                         log_wait_commit(journal, tid);
 173                         goto out_return_1;
 174                 }
 175
 176                 /*
 177                  * AKPM: I think the buffer_jbddirty test is redundant - it
 178                  * shouldn't have NULL b_transaction?
 179                  */
 180                 next_jh = jh->b_cpnext;
 181                 if (!buffer_dirty(bh) && !buffer_jbddirty(bh)) {
 182                         BUFFER_TRACE(bh, "remove from checkpoint");
 183                         __journal_remove_checkpoint(jh);
 184                         jbd_unlock_bh_state(bh);
 185                         journal_remove_journal_head(bh);
 186                         __brelse(bh);
 187                         ret = 1;
 188                 } else {
 189                         jbd_unlock_bh_state(bh);
 190                 }
 191         } while (jh != last_jh);
 192
 193         return ret;
 194 out_return_1:
 195         spin_lock(&journal->j_list_lock);
 196         return 1;
 197 }
 198
 199 #define NR_BATCH        64
 200
 201 static void
 202 __flush_batch(journal_t *journal, struct buffer_head **bhs, int *batch_count)
 203 {
 204         int i;
 205
 206         spin_unlock(&journal->j_list_lock);
 207         ll_rw_block(SWRITE, *batch_count, bhs);
 208         spin_lock(&journal->j_list_lock);
 209         for (i = 0; i < *batch_count; i++) {
 210                 struct buffer_head *bh = bhs[i];
 211                 clear_buffer_jwrite(bh);
 212                 BUFFER_TRACE(bh, "brelse");
 213                 __brelse(bh);
 214         }
 215         *batch_count = 0;
 216 }
 217
 218 /*
 219  * Try to flush one buffer from the checkpoint list to disk.
 220  *
 221  * Return 1 if something happened which requires us to abort the current
 222  * scan of the checkpoint list.
 223  *
 224  * Called with j_list_lock held.
 225  * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 226  */
 227 static int __flush_buffer(journal_t *journal, struct journal_head *jh,
 228                         struct buffer_head **bhs, int *batch_count,
 229                         int *drop_count)
 230 {
 231         struct buffer_head *bh = jh2bh(jh);
 232         int ret = 0;
 233
 234         if (buffer_dirty(bh) && !buffer_locked(bh) && jh->b_jlist == BJ_None) {
 235                 J_ASSERT_JH(jh, jh->b_transaction == NULL);
 236
 237                 /*
 238                  * Important: we are about to write the buffer, and
 239                  * possibly block, while still holding the journal lock.
 240                  * We cannot afford to let the transaction logic start
 241                  * messing around with this buffer before we write it to
 242                  * disk, as that would break recoverability.
 243                  */
 244                 BUFFER_TRACE(bh, "queue");
 245                 get_bh(bh);
 246                 J_ASSERT_BH(bh, !buffer_jwrite(bh));
 247                 set_buffer_jwrite(bh);
 248                 bhs[*batch_count] = bh;
 249                 jbd_unlock_bh_state(bh);
 250                 (*batch_count)++;
 251                 if (*batch_count == NR_BATCH) {
 252                         __flush_batch(journal, bhs, batch_count);
 253                         ret = 1;
 254                 }
 255         } else {
 256                 int last_buffer = 0;
 257                 if (jh->b_cpnext == jh) {
 258                         /* We may be about to drop the transaction.  Tell the
 259                          * caller that the lists have changed.
 260                          */
 261                         last_buffer = 1;
 262                 }
 263                 if (__try_to_free_cp_buf(jh)) {
 264                         (*drop_count)++;
 265                         ret = last_buffer;
 266                 }
 267         }
 268         return ret;
 269 }
 270
 271 /*
 272  * Perform an actual checkpoint.  We don't write out only enough to
 273  * satisfy the current blocked requests: rather we submit a reasonably
 274  * sized chunk of the outstanding data to disk at once for
 275  * efficiency.  __log_wait_for_space() will retry if we didn't free enough.
 276  *
 277  * However, we _do_ take into account the amount requested so that once
 278  * the IO has been queued, we can return as soon as enough of it has
 279  * completed to disk.
 280  *
 281  * The journal should be locked before calling this function.
 282  */
 283 int log_do_checkpoint(journal_t *journal)
 284 {
 285         int result;
 286         int batch_count = 0;
 287         struct buffer_head *bhs[NR_BATCH];
 288
 289         jbd_debug(1, "Start checkpoint\n");
 290
 291         /*
 292          * First thing: if there are any transactions in the log which
 293          * don't need checkpointing, just eliminate them from the
 294          * journal straight away.
 295          */
 296         result = cleanup_journal_tail(journal);
 297         jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
 298         if (result <= 0)
 299                 return result;
 300
 301         /*
 302          * OK, we need to start writing disk blocks.  Try to free up a
 303          * quarter of the log in a single checkpoint if we can.
 304          */
 305         /*
 306          * AKPM: check this code.  I had a feeling a while back that it
 307          * degenerates into a busy loop at unmount time.
 308          */
 309         spin_lock(&journal->j_list_lock);
 310         while (journal->j_checkpoint_transactions) {
 311                 transaction_t *transaction;
 312                 struct journal_head *jh, *last_jh, *next_jh;
 313                 int drop_count = 0;
 314                 int cleanup_ret, retry = 0;
 315                 tid_t this_tid;
 316
 317                 transaction = journal->j_checkpoint_transactions;
 318                 this_tid = transaction->t_tid;
 319                 jh = transaction->t_checkpoint_list;
 320                 last_jh = jh->b_cpprev;
 321                 next_jh = jh;
 322                 do {
 323                         struct buffer_head *bh;
 324
 325                         jh = next_jh;
 326                         next_jh = jh->b_cpnext;
 327                         bh = jh2bh(jh);
 328                         if (!jbd_trylock_bh_state(bh)) {
 329                                 jbd_sync_bh(journal, bh);
 330                                 spin_lock(&journal->j_list_lock);
 331                                 retry = 1;
 332                                 break;
 333                         }
 334                         retry = __flush_buffer(journal, jh, bhs, &batch_count, &drop_count);
 335                         if (cond_resched_lock(&journal->j_list_lock)) {
 336                                 retry = 1;
 337                                 break;
 338                         }
 339                 } while (jh != last_jh && !retry);
 340
 341                 if (batch_count) {
 342                         __flush_batch(journal, bhs, &batch_count);
 343                         retry = 1;
 344                 }
 345
 346                 /*
 347                  * If someone cleaned up this transaction while we slept, we're
 348                  * done
 349                  */
 350                 if (journal->j_checkpoint_transactions != transaction)
 351                         break;
 352                 if (retry)
 353                         continue;
 354                 /*
 355                  * Maybe it's a new transaction, but it fell at the same
 356                  * address
 357                  */
 358                 if (transaction->t_tid != this_tid)
 359                         continue;
 360                 /*
 361                  * We have walked the whole transaction list without
 362                  * finding anything to write to disk.  We had better be
 363                  * able to make some progress or we are in trouble.
 364                  */
 365                 cleanup_ret = __cleanup_transaction(journal, transaction);
 366                 J_ASSERT(drop_count != 0 || cleanup_ret != 0);
 367                 if (journal->j_checkpoint_transactions != transaction)
 368                         break;
 369         }
 370         spin_unlock(&journal->j_list_lock);
 371         result = cleanup_journal_tail(journal);
 372         if (result < 0)
 373                 return result;
 374
 375         return 0;
 376 }
 377
 378 /*
 379  * Check the list of checkpoint transactions for the journal to see if
 380  * we have already got rid of any since the last update of the log tail
 381  * in the journal superblock.  If so, we can instantly roll the
 382  * superblock forward to remove those transactions from the log.
 383  *
 384  * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 385  *
 386  * Called with the journal lock held.
 387  *
 388  * This is the only part of the journaling code which really needs to be
 389  * aware of transaction aborts.  Checkpointing involves writing to the
 390  * main filesystem area rather than to the journal, so it can proceed
 391  * even in abort state, but we must not update the journal superblock if
 392  * we have an abort error outstanding.
 393  */
 394
 395 int cleanup_journal_tail(journal_t *journal)
 396 {
 397         transaction_t * transaction;
 398         tid_t           first_tid;
 399         unsigned long   blocknr, freed;
 400
 401         /* OK, work out the oldest transaction remaining in the log, and
 402          * the log block it starts at.
 403          *
 404          * If the log is now empty, we need to work out which is the
 405          * next transaction ID we will write, and where it will
 406          * start. */
 407
 408         spin_lock(&journal->j_state_lock);
 409         spin_lock(&journal->j_list_lock);
 410         transaction = journal->j_checkpoint_transactions;
 411         if (transaction) {
 412                 first_tid = transaction->t_tid;
 413                 blocknr = transaction->t_log_start;
 414         } else if ((transaction = journal->j_committing_transaction) != NULL) {
 415                 first_tid = transaction->t_tid;
 416                 blocknr = transaction->t_log_start;
 417         } else if ((transaction = journal->j_running_transaction) != NULL) {
 418                 first_tid = transaction->t_tid;
 419                 blocknr = journal->j_head;
 420         } else {
 421                 first_tid = journal->j_transaction_sequence;
 422                 blocknr = journal->j_head;
 423         }
 424         spin_unlock(&journal->j_list_lock);
 425         J_ASSERT(blocknr != 0);
 426
 427         /* If the oldest pinned transaction is at the tail of the log
 428            already then there's not much we can do right now. */
 429         if (journal->j_tail_sequence == first_tid) {
 430                 spin_unlock(&journal->j_state_lock);
 431                 return 1;
 432         }
 433
 434         /* OK, update the superblock to recover the freed space.
 435          * Physical blocks come first: have we wrapped beyond the end of
 436          * the log?  */
 437         freed = blocknr - journal->j_tail;
 438         if (blocknr < journal->j_tail)
 439                 freed = freed + journal->j_last - journal->j_first;
 440
 441         jbd_debug(1,
 442                   "Cleaning journal tail from %d to %d (offset %lu), "
 443                   "freeing %lu\n",
 444                   journal->j_tail_sequence, first_tid, blocknr, freed);
 445
 446         journal->j_free += freed;
 447         journal->j_tail_sequence = first_tid;
 448         journal->j_tail = blocknr;
 449         spin_unlock(&journal->j_state_lock);
 450         if (!(journal->j_flags & JFS_ABORT))
 451                 journal_update_superblock(journal, 1);
 452         return 0;
 453 }
 454
 455
 456 /* Checkpoint list management */
 457
 458 /*
 459  * journal_clean_checkpoint_list
 460  *
 461  * Find all the written-back checkpoint buffers in the journal and release them.
 462  *
 463  * Called with the journal locked.
 464  * Called with j_list_lock held.
 465  * Returns number of bufers reaped (for debug)
 466  */
 467
 468 int __journal_clean_checkpoint_list(journal_t *journal)
 469 {
 470         transaction_t *transaction, *last_transaction, *next_transaction;
 471         int ret = 0;
 472
 473         transaction = journal->j_checkpoint_transactions;
 474         if (transaction == 0)
 475                 goto out;
 476
 477         last_transaction = transaction->t_cpprev;
 478         next_transaction = transaction;
 479         do {
 480                 struct journal_head *jh;
 481
 482                 transaction = next_transaction;
 483                 next_transaction = transaction->t_cpnext;
 484                 jh = transaction->t_checkpoint_list;
 485                 if (jh) {
 486                         struct journal_head *last_jh = jh->b_cpprev;
 487                         struct journal_head *next_jh = jh;
 488
 489                         do {
 490                                 jh = next_jh;
 491                                 next_jh = jh->b_cpnext;
 492                                 /* Use trylock because of the ranknig */
 493                                 if (jbd_trylock_bh_state(jh2bh(jh)))
 494                                         ret += __try_to_free_cp_buf(jh);
 495                                 /*
 496                                  * This function only frees up some memory
 497                                  * if possible so we dont have an obligation
 498                                  * to finish processing. Bail out if preemption
 499                                  * requested:
 500                                  */
 501                                 if (need_resched())
 502                                         goto out;
 503                         } while (jh != last_jh);
 504                 }
 505         } while (transaction != last_transaction);
 506 out:
 507         return ret;
 508 }
 509
 510 /*
 511  * journal_remove_checkpoint: called after a buffer has been committed
 512  * to disk (either by being write-back flushed to disk, or being
 513  * committed to the log).
 514  *
 515  * We cannot safely clean a transaction out of the log until all of the
 516  * buffer updates committed in that transaction have safely been stored
 517  * elsewhere on disk.  To achieve this, all of the buffers in a
 518  * transaction need to be maintained on the transaction's checkpoint
 519  * list until they have been rewritten, at which point this function is
 520  * called to remove the buffer from the existing transaction's
 521  * checkpoint list.
 522  *
 523  * This function is called with the journal locked.
 524  * This function is called with j_list_lock held.
 525  */
 526
 527 void __journal_remove_checkpoint(struct journal_head *jh)
 528 {
 529         transaction_t *transaction;
 530         journal_t *journal;
 531
 532         JBUFFER_TRACE(jh, "entry");
 533
 534         if ((transaction = jh->b_cp_transaction) == NULL) {
 535                 JBUFFER_TRACE(jh, "not on transaction");
 536                 goto out;
 537         }
 538         journal = transaction->t_journal;
 539
 540         __buffer_unlink(jh);
 541
 542         if (transaction->t_checkpoint_list != NULL)
 543                 goto out;
 544         JBUFFER_TRACE(jh, "transaction has no more buffers");
 545
 546         /*
 547          * There is one special case to worry about: if we have just pulled the
 548          * buffer off a committing transaction's forget list, then even if the
 549          * checkpoint list is empty, the transaction obviously cannot be
 550          * dropped!
 551          *
 552          * The locking here around j_committing_transaction is a bit sleazy.
 553          * See the comment at the end of journal_commit_transaction().
 554          */
 555         if (transaction == journal->j_committing_transaction) {
 556                 JBUFFER_TRACE(jh, "belongs to committing transaction");
 557                 goto out;
 558         }
 559
 560         /* OK, that was the last buffer for the transaction: we can now
 561            safely remove this transaction from the log */
 562
 563         __journal_drop_transaction(journal, transaction);
 564
 565         /* Just in case anybody was waiting for more transactions to be
 566            checkpointed... */
 567         wake_up(&journal->j_wait_logspace);
 568 out:
 569         JBUFFER_TRACE(jh, "exit");
 570 }
 571
 572 /*
 573  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 574  * list so that we know when it is safe to clean the transaction out of
 575  * the log.
 576  *
 577  * Called with the journal locked.
 578  * Called with j_list_lock held.
 579  */
 580 void __journal_insert_checkpoint(struct journal_head *jh,
 581                                transaction_t *transaction)
 582 {
 583         JBUFFER_TRACE(jh, "entry");
 584         J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
 585         J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);
 586
 587         jh->b_cp_transaction = transaction;
 588
 589         if (!transaction->t_checkpoint_list) {
 590                 jh->b_cpnext = jh->b_cpprev = jh;
 591         } else {
 592                 jh->b_cpnext = transaction->t_checkpoint_list;
 593                 jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
 594                 jh->b_cpprev->b_cpnext = jh;
 595                 jh->b_cpnext->b_cpprev = jh;
 596         }
 597         transaction->t_checkpoint_list = jh;
 598 }
 599
 600 /*
 601  * We've finished with this transaction structure: adios...
 602  *
 603  * The transaction must have no links except for the checkpoint by this
 604  * point.
 605  *
 606  * Called with the journal locked.
 607  * Called with j_list_lock held.
 608  */
 609
 610 void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 611 {
 612         assert_spin_locked(&journal->j_list_lock);
 613         if (transaction->t_cpnext) {
 614                 transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
 615                 transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
 616                 if (journal->j_checkpoint_transactions == transaction)
 617                         journal->j_checkpoint_transactions =
 618                                 transaction->t_cpnext;
 619                 if (journal->j_checkpoint_transactions == transaction)
 620                         journal->j_checkpoint_transactions = NULL;
 621         }
 622
 623         J_ASSERT(transaction->t_state == T_FINISHED);
 624         J_ASSERT(transaction->t_buffers == NULL);
 625         J_ASSERT(transaction->t_sync_datalist == NULL);
 626         J_ASSERT(transaction->t_forget == NULL);
 627         J_ASSERT(transaction->t_iobuf_list == NULL);
 628         J_ASSERT(transaction->t_shadow_list == NULL);
 629         J_ASSERT(transaction->t_log_list == NULL);
 630         J_ASSERT(transaction->t_checkpoint_list == NULL);
 631         J_ASSERT(transaction->t_updates == 0);
 632         J_ASSERT(journal->j_committing_transaction != transaction);
 633         J_ASSERT(journal->j_running_transaction != transaction);
 634
 635         jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
 636         kfree(transaction);
 637 }