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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Jiang Biao <jiang.biao2@zte.com.cn>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Minchan Kim <minchan@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        "zhong.weidong@zte.com.cn" <zhong.weidong@zte.com.cn>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.14 077/100] fs/mbcache.c: make count_objects()
 more robust
Thread-Topic: [PATCH AUTOSEL for 4.14 077/100] fs/mbcache.c: make
 count_objects() more robust
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Date:   Wed, 24 Jan 2018 04:15:04 +0000
Message-ID: <20180124041414.32065-77-alexander.levin@microsoft.com>
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From: Jiang Biao <jiang.biao2@zte.com.cn>

[ Upstream commit d5dabd633922ac5ee5bcc67748f7defb8b211469 ]

When running ltp stress test for 7*24 hours, vmscan occasionally emits
the following warning continuously:

  mb_cache_scan+0x0/0x3f0 negative objects to delete
  nr=3D-9232265467809300450
  ...

Tracing shows the freeable(mb_cache_count returns) is -1, which causes
the continuous accumulation and overflow of total_scan.

This patch makes sure that mb_cache_count() cannot return a negative
value, which makes the mbcache shrinker more robust.

Link: http://lkml.kernel.org/r/1511753419-52328-1-git-send-email-jiang.biao=
2@zte.com.cn
Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <zhong.weidong@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 fs/mbcache.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index d818fd236787..b8b8b9ced9f8 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -269,6 +269,9 @@ static unsigned long mb_cache_count(struct shrinker *sh=
rink,
 	struct mb_cache *cache =3D container_of(shrink, struct mb_cache,
 					      c_shrink);
=20
+	/* Unlikely, but not impossible */
+	if (unlikely(cache->c_entry_count < 0))
+		return 0;
 	return cache->c_entry_count;
 }
=20
--=20
2.11.0