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jbd2: fix fsync() tid wraparound bug

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If an application program does not make any changes to the indirect
blocks or extent tree, i_datasync_tid will not get updated.  If there
are enough commits (i.e., 2**31) such that tid_geq()'s calculations
wrap, and there isn't a currently active transaction at the time of
the fdatasync() call, this can end up triggering a BUG_ON in
fs/jbd2/commit.c:

	J_ASSERT(journal->j_running_transaction != NULL);

It's pretty rare that this can happen, since it requires the use of
fdatasync() plus *very* frequent and excessive use of fsync().  But
with the right workload, it can.

We fix this by replacing the use of tid_geq() with an equality test,
since there's only one valid transaction id that we is valid for us to
wait until it is commited: namely, the currently running transaction
(if it exists).

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2011-05-01 18:16:26 -04:00
parent 59802db074
commit deeeaf13b2
1 changed files with 13 additions and 3 deletions
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16
fs/jbd2/journal.c
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@ -479,9 +479,12 @@ int __jbd2_log_space_left(journal_t *journal)
int __jbd2_log_start_commit(journal_t *journal, tid_t target) int __jbd2_log_start_commit(journal_t *journal, tid_t target)
{ {
/* /*
* Are we already doing a recent enough commit? * The only transaction we can possibly wait upon is the
* currently running transaction (if it exists). Otherwise,
* the target tid must be an old one.
*/ */
if (!tid_geq(journal->j_commit_request, target)) { if (journal->j_running_transaction &&
journal->j_running_transaction->t_tid == target) {
/* /*
* We want a new commit: OK, mark the request and wakeup the * We want a new commit: OK, mark the request and wakeup the
* commit thread. We do _not_ do the commit ourselves. * commit thread. We do _not_ do the commit ourselves.
@ -493,7 +496,14 @@ int __jbd2_log_start_commit(journal_t *journal, tid_t target)
journal->j_commit_sequence); journal->j_commit_sequence);
wake_up(&journal->j_wait_commit); wake_up(&journal->j_wait_commit);
return 1; return 1;
} } else if (!tid_geq(journal->j_commit_request, target))
/* This should never happen, but if it does, preserve
the evidence before kjournald goes into a loop and
increments j_commit_sequence beyond all recognition. */
WARN(1, "jbd: bad log_start_commit: %u %u %u %u\n",
journal->j_commit_request, journal->j_commit_sequence,
target, journal->j_running_transaction ?
journal->j_running_transaction->t_tid : 0);
return 0; return 0;
} }