From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f174.google.com ([74.125.82.174]:60681 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751251Ab2HNOTI (ORCPT ); Tue, 14 Aug 2012 10:19:08 -0400 Message-ID: <502A5CDA.2080806@gmail.com> Date: Tue, 14 Aug 2012 16:12:42 +0200 From: Marco Stornelli MIME-Version: 1.0 To: Liu Bo CC: liub.liubo@gmail.com, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH RFC] Btrfs: fix deadlock between sys_sync and freeze References: <1344920474-10014-1-git-send-email-liub.liubo@gmail.com> <502A4BB2.6000404@gmail.com> <502A5849.9040602@oracle.com> In-Reply-To: <502A5849.9040602@oracle.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Il 14/08/2012 15:53, Liu Bo ha scritto: > On 08/14/2012 08:59 PM, Marco Stornelli wrote: >> Il 14/08/2012 07:01, liub.liubo@gmail.com ha scritto: >>> From: Liu Bo >>> >>> I found this while testing xfstests 068, the story is >>> >>> t1 t2 >>> sys_sync thaw_super >>> iterate_supers >>> down_read(sb->s_umount) down_write(sb->s_umount) --->wait for t1 >>> sync_fs (with wait mode) >>> start_transaction >>> sb_start_intwrite --------------------> wait for t2 to set s_writers.frozen to SB_UNFROZEN >>> >>> In this patch, I add an helper sb_start_intwrite_trylock() and use it before we >>> start_transaction in sync_fs() with wait mode so that we won't hit the deadlock. >>> >> >> IMHO, we should avoid to call the sync operation on a frozen fs. The freeze operation, indeed, already include a sync operation. >> According to man page, no other operation should modify the fs after the freeze. >> So for me the modification is inside sync_filesystem (and sync_one_sb). > > Do you mean that we should add the trylock check in sync_filesystem? > > But it seems to be useless because we already run into down_read(sb->s_umount) before starting sync_one_sb(). > > thanks, > liubo > I meant that we should check if there are in a "complete" freeze state (according to the "states" of a freeze transaction) and simply skip the sync operation. Marco