Patchwork [2/2] jbd: fix fsync() tid wraparound bug

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Submitter Theodore Ts'o
Date April 26, 2011, 12:23 a.m.
Message ID <1303777411-1316-2-git-send-email-tytso@mit.edu>
Download mbox | patch
Permalink /patch/92828/
State Superseded
Headers show

Comments

Theodore Ts'o - April 26, 2011, 12:23 a.m.
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/jbd/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/jbd/journal.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

Patch

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index b3713af..6b51233 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -437,9 +437,12 @@  int __log_space_left(journal_t *journal)
 int __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.