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authorTheodore Ts'o <tytso@mit.edu>2013-04-03 22:02:52 -0400
committerTheodore Ts'o <tytso@mit.edu>2013-04-03 22:02:52 -0400
commitd76a3a77113db020d9bb1e894822869410450bd9 (patch)
tree3e73e273fd8c8e09b2bb87417615d391491eb38e /fs/jbd2
parentb10a44c369d7b8a28825f1fd24f13dc31c2e3a25 (diff)
ext4/jbd2: don't wait (forever) for stale tid caused by wraparound
In the case where an inode has a very stale transaction id (tid) in i_datasync_tid or i_sync_tid, it's possible that after a very large (2**31) number of transactions, that the tid number space might wrap, causing tid_geq()'s calculations to fail. Commit deeeaf13 "jbd2: fix fsync() tid wraparound bug", later modified by commit e7b04ac0 "jbd2: don't wake kjournald unnecessarily", attempted to fix this problem, but it only avoided kjournald spinning forever by fixing the logic in jbd2_log_start_commit(). Unfortunately, in the codepaths in fs/ext4/fsync.c and fs/ext4/inode.c that might call jbd2_log_start_commit() with a stale tid, those functions will subsequently call jbd2_log_wait_commit() with the same stale tid, and then wait for a very long time. To fix this, we replace the calls to jbd2_log_start_commit() and jbd2_log_wait_commit() with a call to a new function, jbd2_complete_transaction(), which will correctly handle stale tid's. As a bonus, jbd2_complete_transaction() will avoid locking j_state_lock for writing unless a commit needs to be started. This should have a small (but probably not measurable) improvement for ext4's scalability. Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Reported-by: Ben Hutchings <ben@decadent.org.uk> Reported-by: George Barnett <gbarnett@atlassian.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'fs/jbd2')
-rw-r--r--fs/jbd2/journal.c31
1 files changed, 31 insertions, 0 deletions
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index ed10991ab006..886ec2faa9b4 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -710,6 +710,37 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
}
/*
+ * When this function returns the transaction corresponding to tid
+ * will be completed. If the transaction has currently running, start
+ * committing that transaction before waiting for it to complete. If
+ * the transaction id is stale, it is by definition already completed,
+ * so just return SUCCESS.
+ */
+int jbd2_complete_transaction(journal_t *journal, tid_t tid)
+{
+ int need_to_wait = 1;
+
+ read_lock(&journal->j_state_lock);
+ if (journal->j_running_transaction &&
+ journal->j_running_transaction->t_tid == tid) {
+ if (journal->j_commit_request != tid) {
+ /* transaction not yet started, so request it */
+ read_unlock(&journal->j_state_lock);
+ jbd2_log_start_commit(journal, tid);
+ goto wait_commit;
+ }
+ } else if (!(journal->j_committing_transaction &&
+ journal->j_committing_transaction->t_tid == tid))
+ need_to_wait = 0;
+ read_unlock(&journal->j_state_lock);
+ if (!need_to_wait)
+ return 0;
+wait_commit:
+ return jbd2_log_wait_commit(journal, tid);
+}
+EXPORT_SYMBOL(jbd2_complete_transaction);
+
+/*
* Log buffer allocation routines:
*/