[Devel] [PATCH vz8] mm: check shrinker is memcg-aware in register_shrinker_prepared()

[Andrey Ryabinin]

From: Kirill Tkhai <ktkhai at virtuozzo.com>

There is a sad BUG introduced in patch adding SHRINKER_REGISTERING.
shrinker_idr business is only for memcg-aware shrinkers.  Only such type
of shrinkers have id and they must be finaly installed via idr_replace()
in this function.  For !memcg-aware shrinkers we never initialize
shrinker->id field.

But there are all types of shrinkers passed to idr_replace(), and every
!memcg-aware shrinker with random ID (most probably, its id is 0)
replaces memcg-aware shrinker pointed by the ID in IDR.

This patch fixes the problem.

Link: http://lkml.kernel.org/r/8ff8a793-8211-713a-4ed9-d6e52390c2fc@virtuozzo.com
Fixes: 7e010df53c80 "mm: use special value SHRINKER_REGISTERING instead of list_empty() check"
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Reported-by: <syzbot+d5f648a1bfe15678786b at syzkaller.appspotmail.com>
Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: Josef Bacik <jbacik at fb.com>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Michal Hocko <mhocko at suse.com>
Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Cc: Shakeel Butt <shakeelb at google.com>
Cc: <syzkaller-bugs at googlegroups.com>
Cc: Huang Ying <ying.huang at intel.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit 8df4a44cc46bf9dcfb80a37a59ae5dea2232dc58)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/vmscan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 580c8c6843b9..52f5e9203ebe 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -376,7 +376,8 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
 #ifdef CONFIG_MEMCG_KMEM
-	idr_replace(&shrinker_idr, shrinker, shrinker->id);
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		idr_replace(&shrinker_idr, shrinker, shrinker->id);
 #endif
 	up_write(&shrinker_rwsem);
 }
-- 
2.24.1