[dm-devel] [PATCH] dm-raid: unsynced raid snapshot creation/deletion causes panic (work queue teardown race)

[heinzm at redhat.com]

From: Heinz Mauelshagen <heinzm at redhat.com>

This patch avoids oopses caused by a callback racing
with the destrution of a mapping.


Signed-off-by: Heinz Mauelshagen <heinzm at redhat.com>
Tested-by: Heinz Mauelshagen <heinzm at redhat.com>


---
 drivers/md/dm-raid.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 88e4c7f..fc4bc83 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -1614,6 +1614,17 @@ static void raid_presuspend(struct dm_target *ti)
 {
 	struct raid_set *rs = ti->private;
 
+	/*
+	 * Address a teardown race when calling
+	 * raid_(pre|post)suspend followed by raid_dtr:
+	 *
+	 * MD's call chain md_stop_writes()->md_reap_sync_thread()
+	 * causes work to be queued on the md_misc_wq queue
+	 * not flushing it, hence the callback can occur after
+	 * a potential destruction of the raid set causing an oops.
+	 */
+	rs->md.event_work.func = NULL;
+
 	md_stop_writes(&rs->md);
 }
 
@@ -1684,6 +1695,13 @@ static void raid_resume(struct dm_target *ti)
 {
 	struct raid_set *rs = ti->private;
 
+	/*
+	 * See "Address a teardown race" in raid_presuspend()
+	 *
+	 * Reenable the worker function.
+	 */
+	rs->md.event_work.func = do_table_event;
+
 	set_bit(MD_CHANGE_DEVS, &rs->md.flags);
 	if (!rs->bitmap_loaded) {
 		bitmap_load(&rs->md);
-- 
2.1.0