From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f66.google.com ([209.85.215.66]:45834 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbdJGL4o (ORCPT ); Sat, 7 Oct 2017 07:56:44 -0400 Date: Sat, 7 Oct 2017 14:56:40 +0300 From: Vladimir Davydov To: Michal Hocko Cc: Jia-Ju Bai , viro@zeniv.linux.org.uk, torbjorn.lindh@gopta.se, rgooch@atnf.csiro.au, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [BUG] fs/super: a possible sleep-in-atomic bug in put_super Message-ID: <20171007115640.w3m6vxxrglcbeutl@esperanza> References: <06badf5e-292d-ef63-7499-6888dec1b9b0@163.com> <20171006090604.m5oxcyb2xtllpmpu@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171006090604.m5oxcyb2xtllpmpu@dhcp22.suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Hello, On Fri, Oct 06, 2017 at 11:06:04AM +0200, Michal Hocko wrote: > On Fri 06-10-17 16:59:18, Jia-Ju Bai wrote: > > According to fs/super.c, the kernel may sleep under a spinlock. > > The function call path is: > > put_super (acquire the spinlock) > > __put_super > > destroy_super > > list_lru_destroy > > list_lru_unregister > > mutex_lock --> may sleep > > memcg_get_cache_ids > > down_read --> may sleep > > > > This bug is found by my static analysis tool and my code review. This is false-positive: by the time we get to destroy_super(), the lru lists have already been destroyed - see deactivate_locked_super() - so list_lru_destroy() will retrun right away without attempting to take any locks. That's why there's no lockdep warnings regarding this issue. I think we can move list_lru_destroy() to destroy_super_work() to suppress this warning. Not sure if it's really worth the trouble though. Thanks, Vladimir