Revert "dm bufio: fix deadlock with loop device"

Mikulas Patocka · gregkh · commit b608a5a238d5 · 2019-08-29T08:28:49.000+02:00
commit cf3591e upstream. Revert the commit bd293d0. The proper fix has been made available with commit d0a255e ("loop: set PF_MEMALLOC_NOIO for the worker thread"). Note that the fix offered by commit bd293d0 doesn't really prevent the deadlock from occuring - if we look at the stacktrace reported by Junxiao Bi, we see that it hangs in bit_wait_io and not on the mutex - i.e. it has already successfully taken the mutex. Changing the mutex from mutex_lock to mutex_trylock won't help with deadlocks that happen afterwards. PID: 474 TASK: ffff8813e11f4600 CPU: 10 COMMAND: "kswapd0" #0 [ffff8813dedfb938] __schedule at ffffffff8173f405 #1 [ffff8813dedfb990] schedule at ffffffff8173fa27 #2 [ffff8813dedfb9b0] schedule_timeout at ffffffff81742fec #3 [ffff8813dedfba60] io_schedule_timeout at ffffffff8173f186 #4 [ffff8813dedfbaa0] bit_wait_io at ffffffff8174034f #5 [ffff8813dedfbac0] __wait_on_bit at ffffffff8173fec8 #6 [ffff8813dedfbb10] out_of_line_wait_on_bit at ffffffff8173ff81 #7 [ffff8813dedfbb90] __make_buffer_clean at ffffffffa038736f [dm_bufio] #8 [ffff8813dedfbbb0] __try_evict_buffer at ffffffffa0387bb8 [dm_bufio] #9 [ffff8813dedfbbd0] dm_bufio_shrink_scan at ffffffffa0387cc3 [dm_bufio] #10 [ffff8813dedfbc40] shrink_slab at ffffffff811a87ce #11 [ffff8813dedfbd30] shrink_zone at ffffffff811ad778 #12 [ffff8813dedfbdc0] kswapd at ffffffff811ae92f #13 [ffff8813dedfbec0] kthread at ffffffff810a8428 #14 [ffff8813dedfbf50] ret_from_fork at ffffffff81745242 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: stable@vger.kernel.org Fixes: bd293d0 ("dm bufio: fix deadlock with loop device") Depends-on: d0a255e ("loop: set PF_MEMALLOC_NOIO for the worker thread") Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
@@ -1602,7 +1602,9 @@ dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 	unsigned long freed;
 
 	c = container_of(shrink, struct dm_bufio_client, shrinker);
-	if (!dm_bufio_trylock(c))
+	if (sc->gfp_mask & __GFP_FS)
+		dm_bufio_lock(c);
+	else if (!dm_bufio_trylock(c))
 		return SHRINK_STOP;
 
 	freed  = __scan(c, sc->nr_to_scan, sc->gfp_mask);
