From: Kirill Tkhai <ktkhai@virtuozzo.com>
Date: Wed, 22 Aug 2018 04:51:49 +0000 (-0700)
Subject: mm: check shrinker is memcg-aware in register_shrinker_prepared()
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=8df4a44cc46bf9dcfb80a37a59ae5dea2232dc58;p=openwrt%2Fstaging%2Fblogic.git

mm: check shrinker is memcg-aware in register_shrinker_prepared()

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@virtuozzo.com>
Reported-by: <syzbot+d5f648a1bfe15678786b@syzkaller.appspotmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: <syzkaller-bugs@googlegroups.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4375b1e9bd56..3c6e2bfee427 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -408,7 +408,8 @@ 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);
 }