From: Theodore Ts'o Subject: Re: [PATCH v2] fs/mbcache: make sure mb_cache_count() not return negative value. Date: Tue, 9 Jan 2018 23:58:12 -0500 Message-ID: <20180110045812.GD5809@thunk.org> References: <1515454691-69220-1-git-send-email-jiang.biao2@zte.com.cn> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, ebiggers@google.com, akpm@linux-foundation.org, jack@suse.cz, zhong.weidong@zte.com.cn To: Jiang Biao Return-path: Received: from imap.thunk.org ([74.207.234.97]:57510 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932424AbeAJE6R (ORCPT ); Tue, 9 Jan 2018 23:58:17 -0500 Content-Disposition: inline In-Reply-To: <1515454691-69220-1-git-send-email-jiang.biao2@zte.com.cn> Sender: linux-ext4-owner@vger.kernel.org List-ID: I think I've found the cause of it, but having a sanity check is a good idea. I've simplified the patch and its description, though. This is what I have in my tree. - Ted commit 252194e48f00d146de303822bba8c3568ca127cd Author: Jiang Biao Date: Tue Jan 9 23:57:52 2018 -0500 mbcache: make sure c_entry_count is not decremented past zero Signed-off-by: Jiang Biao Signed-off-by: Theodore Ts'o CC: Eric Biggers CC: Andrew Morton CC: Jan Kara diff --git a/fs/mbcache.c b/fs/mbcache.c index 0851af5c1c3d..f2f15b747bed 100644 --- a/fs/mbcache.c +++ b/fs/mbcache.c @@ -239,7 +239,9 @@ 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 (!WARN_ONCE(cache->c_entry_count == 0, + "mbcache: attempt to decrement c_entry_count past zero")) + cache->c_entry_count--; atomic_dec(&entry->e_refcnt); } spin_unlock(&cache->c_list_lock);