fs/mbcache.c: make count_objects() more robust
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=-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.biao2@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>
diff --git a/fs/mbcache.c b/fs/mbcache.c
index d818fd2..b8b8b9c 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -269,6 +269,9 @@ static unsigned long mb_cache_count(struct shrinker *shrink,
struct mb_cache *cache = container_of(shrink, struct mb_cache,
c_shrink);
+ /* Unlikely, but not impossible */
+ if (unlikely(cache->c_entry_count < 0))
+ return 0;
return cache->c_entry_count;
}