diff options
authorJun'ichi Nomura <j-nomura@ce.jp.nec.com>2014-07-08 00:55:14 +0000
committerMike Snitzer <snitzer@redhat.com>2014-07-10 16:44:15 -0400
commit7a7a3b45fed9a144dbf766ee842a4c5d0632b81d (patch)
parent10f1d5d111e8aed46a0f1179faf9a3cf422f689e (diff)
dm mpath: fix IO hang due to logic bug in multipath_busy
Commit e80991773 ("dm mpath: push back requests instead of queueing") modified multipath_busy() to return true if !pg_ready(). pg_ready() checks the current state of the multipath device and may return false even if a new IO is needed to change the state. Bart Van Assche reported that he had multipath IO lockup when he was performing cable pull tests. Analysis showed that the multipath device had a single path group with both paths active, but that the path group itself was not active. During the multipath device state transitions 'queue_io' got set but nothing could clear it. Clearing 'queue_io' only happens in __choose_pgpath(), but it won't be called if multipath_busy() returns true due to pg_ready() returning false when 'queue_io' is set. As such the !pg_ready() check in multipath_busy() is wrong because new IO will not be sent to multipath target and the multipath state change won't happen. That results in multipath IO lockup. The intent of multipath_busy() is to avoid unnecessary cycles of dequeue + request_fn + requeue if it is known that the multipath device will requeue. Such "busy" situations would be: - path group is being activated - there is no path and the multipath is setup to requeue if no path Fix multipath_busy() to return "busy" early only for these specific situations. Reported-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Cc: stable@vger.kernel.org # v3.15
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 3f6fd9d33ba..f4167b013d9 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1611,8 +1611,9 @@ static int multipath_busy(struct dm_target *ti)
spin_lock_irqsave(&m->lock, flags);
- /* pg_init in progress, requeue until done */
- if (!pg_ready(m)) {
+ /* pg_init in progress or no paths available */
+ if (m->pg_init_in_progress ||
+ (!m->nr_valid_paths && m->queue_if_no_path)) {
busy = 1;
goto out;