dquot_writeback_dquots() expects s_umount semaphore to be held to
protect it from other concurrent quota operations. reiserfs_sync_fs()
can call dquot_writeback_dquots() without holding s_umount semaphore
when called from flush_old_commits().
Fix the problem by grabbing s_umount in flush_old_commits(). However we
have to be careful and use only trylock since reiserfs_cancel_old_sync()
can be waiting for flush_old_commits() to complete while holding
s_umount semaphore. Possible postponing of sync work is not a big deal
though as that is only an opportunistic flush.
Fixes: 9d1ccbe70e0b14545caad12dc73adb3605447df0
Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/reiserfs/super.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index 91cf5cbd6332..f536e12c4b1d 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -89,6 +89,19 @@ static void flush_old_commits(struct work_struct *work)
sbi = container_of(work, struct reiserfs_sb_info, old_work.work);
s = sbi->s_journal->j_work_sb;
+ /*
+ * We need s_umount for protecting quota writeback. We have to use
+ * trylock as reiserfs_cancel_old_flush() may be waiting for this work
+ * to complete with s_umount held.
+ */
+ if (!down_read_trylock(&s->s_umount)) {
+ /* Requeue work if we are not cancelling it */
+ spin_lock(&sbi->old_work_lock);
+ if (sbi->work_queued == 1)
+ queue_delayed_work(system_long_wq, &sbi->old_work, HZ);
+ spin_unlock(&sbi->old_work_lock);
+ return;
+ }
spin_lock(&sbi->old_work_lock);
/* Avoid clobbering the cancel state... */
if (sbi->work_queued == 1)
@@ -96,6 +109,7 @@ static void flush_old_commits(struct work_struct *work)
spin_unlock(&sbi->old_work_lock);
reiserfs_sync_fs(s, 1);
+ up_read(&s->s_umount);
}
void reiserfs_schedule_old_flush(struct super_block *s)
--
2.10.2
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