From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2() Date: Fri, 13 Feb 2009 06:41:35 +0000 Message-ID: <20090213064135.GJ28946@ZenIV.linux.org.uk> References: <20090209093414.GU28946@ZenIV.linux.org.uk> <499013CC.2060808@cn.fujitsu.com> <4993BD5D.2020707@cn.fujitsu.com> <20090212062442.GE28946@ZenIV.linux.org.uk> <4993C2A0.3050507@cn.fujitsu.com> <4993C7C2.4060100@cn.fujitsu.com> <20090212070729.GF28946@ZenIV.linux.org.uk> <4995007D.7040101@cn.fujitsu.com> <20090213054751.GI28946@ZenIV.linux.org.uk> <49950F3D.3030704@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <49950F3D.3030704-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Li Zefan Cc: containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, LKML , Paul Menage , Andrew Morton , Arjan van de Ven List-Id: containers.vger.kernel.org On Fri, Feb 13, 2009 at 02:12:13PM +0800, Li Zefan wrote: > Al Viro wrote: > > On Fri, Feb 13, 2009 at 01:09:17PM +0800, Li Zefan wrote: > > > >> I ran following testcase, and triggered the warning in 1 hour: > >> > >> thread 1: > >> for ((; ;)) > >> { > >> mount --bind /cgroup /mnt > /dev/null 2>&1 > >> umount /mnt > /dev/null 2>&1 > >> } > >> > >> tread 2: > >> for ((; ;)) > >> { > >> mount -t cgroup -o cpu xxx /cgroup > /dev/null 2>&1 > >> mkdir /cgroup/0 > /dev/null 2>&1 > >> rmdir /cgroup/0 > /dev/null 2>&1 > >> umount -l /cgroup > /dev/null 2>&1 > >> } > > > > Wow. You know, at that point these redirects could probably be removed. > > Ah, yes. > > > If anything in there ends up producing an output, we very much want to > > see that. Actually, I'd even make that > > mount --bind /cgroup/mnt || (echo mount1: ; date) > > etc., so we'd see when do they fail and which one fails (if any)... > > > > Which umount has failed in the above, BTW? > > > > > > the first one sometimes failed, and the second one hasn't failed: > mount: wrong fs type, bad option, bad superblock on /cgroup, > missing codepage or helper program, or other error > In some cases useful info is found in syslog - try > dmesg | tail or so > > mount1 Hold on. In your last example the first one was doing mount --bind; has _that_ failed? Oh, wait... It can fail, all right, if lookup on /cgroup gives you your filesystem with the second thread managing to detach it before we get the namespace_sem. Then we'll fail that way - and clean up properly. Oh, well... The original question still stands: with those two scripts, which umount produces that WARN_ON? The trivial way to check would be to have a copy of /sbin/umount under a different name and use _that_ in one of the threads instead of umount. Then reproduce the WARN_ON and look at the process name in dmesg... From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759827AbZBMGl6 (ORCPT ); Fri, 13 Feb 2009 01:41:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751063AbZBMGls (ORCPT ); Fri, 13 Feb 2009 01:41:48 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:60076 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750928AbZBMGlr (ORCPT ); Fri, 13 Feb 2009 01:41:47 -0500 Date: Fri, 13 Feb 2009 06:41:35 +0000 From: Al Viro To: Li Zefan Cc: containers@lists.osdl.org, Paul Menage , Arjan van de Ven , Andrew Morton , LKML Subject: Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2() Message-ID: <20090213064135.GJ28946@ZenIV.linux.org.uk> References: <20090209093414.GU28946@ZenIV.linux.org.uk> <499013CC.2060808@cn.fujitsu.com> <4993BD5D.2020707@cn.fujitsu.com> <20090212062442.GE28946@ZenIV.linux.org.uk> <4993C2A0.3050507@cn.fujitsu.com> <4993C7C2.4060100@cn.fujitsu.com> <20090212070729.GF28946@ZenIV.linux.org.uk> <4995007D.7040101@cn.fujitsu.com> <20090213054751.GI28946@ZenIV.linux.org.uk> <49950F3D.3030704@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49950F3D.3030704@cn.fujitsu.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 13, 2009 at 02:12:13PM +0800, Li Zefan wrote: > Al Viro wrote: > > On Fri, Feb 13, 2009 at 01:09:17PM +0800, Li Zefan wrote: > > > >> I ran following testcase, and triggered the warning in 1 hour: > >> > >> thread 1: > >> for ((; ;)) > >> { > >> mount --bind /cgroup /mnt > /dev/null 2>&1 > >> umount /mnt > /dev/null 2>&1 > >> } > >> > >> tread 2: > >> for ((; ;)) > >> { > >> mount -t cgroup -o cpu xxx /cgroup > /dev/null 2>&1 > >> mkdir /cgroup/0 > /dev/null 2>&1 > >> rmdir /cgroup/0 > /dev/null 2>&1 > >> umount -l /cgroup > /dev/null 2>&1 > >> } > > > > Wow. You know, at that point these redirects could probably be removed. > > Ah, yes. > > > If anything in there ends up producing an output, we very much want to > > see that. Actually, I'd even make that > > mount --bind /cgroup/mnt || (echo mount1: ; date) > > etc., so we'd see when do they fail and which one fails (if any)... > > > > Which umount has failed in the above, BTW? > > > > > > the first one sometimes failed, and the second one hasn't failed: > mount: wrong fs type, bad option, bad superblock on /cgroup, > missing codepage or helper program, or other error > In some cases useful info is found in syslog - try > dmesg | tail or so > > mount1 Hold on. In your last example the first one was doing mount --bind; has _that_ failed? Oh, wait... It can fail, all right, if lookup on /cgroup gives you your filesystem with the second thread managing to detach it before we get the namespace_sem. Then we'll fail that way - and clean up properly. Oh, well... The original question still stands: with those two scripts, which umount produces that WARN_ON? The trivial way to check would be to have a copy of /sbin/umount under a different name and use _that_ in one of the threads instead of umount. Then reproduce the WARN_ON and look at the process name in dmesg...