When a full journal commit is on-going, any fast commit has to be enqueued
into a different queue: FC_Q_STAGING instead of FC_Q_MAIN. This enqueueing
is done only once, i.e. if an inode is already queued in a previous fast
commit entry it won't be enqueued again. However, if a full commit starts
_after_ the inode is enqueued into FC_Q_MAIN, the next fast commit needs to
be done into FC_Q_STAGING. And this is not being done in function
ext4_fc_track_template().
This patch fixes the issue by re-enqueuing an inode into the STAGING queue
during the fast commit clean-up callback when doing a full commit. However,
to prevent a race with a fast-commit, the clean-up callback has to be called
with the journal locked.
This bug was found using fstest generic/047. This test creates several 32k
bytes files, sync'ing each of them after it's creation, and then shutting
down the filesystem. Some data may be loss in this operation; for example a
file may have it's size truncated to zero.
Suggested-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Luis Henriques (SUSE) <luis.henriques@xxxxxxxxx>
---
Hi!
And here's another attempt to fix this bug. The most significant change is
that now it doesn't assume a 'special' meaning for a tid of '0'. Which is
a wrong assumption as Jan has shown.
I've also added a Suggested-by: tag, although Jan pretty much owns this
patch -- I have simply tested it and sent it out!
fs/ext4/fast_commit.c | 15 ++++++++++++++-
fs/jbd2/journal.c | 2 +-
2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 3926a05eceee..df71fd5b1fed 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -1288,8 +1288,21 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
list_del_init(&iter->i_fc_list);
ext4_clear_inode_state(&iter->vfs_inode,
EXT4_STATE_FC_COMMITTING);
- if (tid_geq(tid, iter->i_sync_tid))
+ if (tid_geq(tid, iter->i_sync_tid)) {
ext4_fc_reset_inode(&iter->vfs_inode);
+ } else if (full) {
+ /*
+ * We are called after a full commit, inode has been
+ * modified while the commit was running. Re-enqueue
+ * the inode into STAGING, which will then be splice
+ * back into MAIN. This cannot happen during
+ * fastcommit because the journal is locked all the
+ * time in that case (and tid doesn't increase so
+ * tid check above isn't reliable).
+ */
+ list_add_tail(&EXT4_I(&iter->vfs_inode)->i_fc_list,
+ &sbi->s_fc_q[FC_Q_STAGING]);
+ }
/* Make sure EXT4_STATE_FC_COMMITTING bit is clear */
smp_mb();
#if (BITS_PER_LONG < 64)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 1ebf2393bfb7..291a431f8aaf 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -740,9 +740,9 @@ EXPORT_SYMBOL(jbd2_fc_begin_commit);
*/
static int __jbd2_fc_end_commit(journal_t *journal, tid_t tid, bool fallback)
{
- jbd2_journal_unlock_updates(journal);
if (journal->j_fc_cleanup_callback)
journal->j_fc_cleanup_callback(journal, 0, tid);
+ jbd2_journal_unlock_updates(journal);
write_lock(&journal->j_state_lock);
journal->j_flags &= ~JBD2_FAST_COMMIT_ONGOING;
if (fallback)
