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
---
fs/jbd2/journal.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index e0ec3db..a5daa5a 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -479,9 +479,12 @@ int __jbd2_log_space_left(journal_t *journal)
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
* commit thread. We do _not_ do the commit ourselves.
@@ -493,6 +496,17 @@ int __jbd2_log_start_commit(journal_t *journal, tid_t target)
journal->j_commit_sequence);
wake_up(&journal->j_wait_commit);
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. */
+ pr_err("jbd2: bad log_start_commit: %u %u %u\n",
+ journal->j_commit_request, journal->j_commit_sequence,
+ target);
+ if (journal->j_running_transaction)
+ pr_err("jbd2: current txn: %u\n",
+ journal->j_running_transaction->t_tid);
+ WARN_ON(1);
}
return 0;
}
--
1.7.3.1
--
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