From: Jiang Biao Subject: [PATCH v2] fs/mbcache: make sure mb_cache_count() not return negative value. Date: Tue, 9 Jan 2018 07:38:11 +0800 Message-ID: <1515454691-69220-1-git-send-email-jiang.biao2@zte.com.cn> Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, ebiggers@google.com, akpm@linux-foundation.org, jack@suse.cz, jiang.biao2@zte.com.cn, zhong.weidong@zte.com.cn To: linux-fsdevel@vger.kernel.org Return-path: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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 .... Trace info 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() not return a negative value, which makes the mbcache shrinker more robust. Signed-off-by: Jiang Biao CC: "Theodore Ts'o" CC: Eric Biggers CC: Andrew Morton CC: Jan Kara --- fs/mbcache.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/mbcache.c b/fs/mbcache.c index b8b8b9c..2a800e3 100644 --- a/fs/mbcache.c +++ b/fs/mbcache.c @@ -238,7 +238,11 @@ void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value) spin_lock(&cache->c_list_lock); if (!list_empty(&entry->e_list)) { list_del_init(&entry->e_list); - cache->c_entry_count--; + if (cache->c_entry_count > 0) + cache->c_entry_count--; + else + WARN_ONCE(1, "mbcache: Entry count " + "going negative!\n"); atomic_dec(&entry->e_refcnt); } spin_unlock(&cache->c_list_lock); -- 2.7.4