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Date: Fri, 13 Feb 2009 14:12:13 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: Al Viro <viro@ZenIV.linux.org.uk>
CC: containers@lists.osdl.org, Paul Menage <menage@google.com>,
       Arjan van de Ven <arjan@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636	mntput_no_expire+0xac/0xf2()
References: <49617D35.4040805@cn.fujitsu.com> <20090209004046.3ce1dde0.akpm@linux-foundation.org> <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>
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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
Fri Feb 13 14:05:37 CST 2009
umount: /mnt: not mounted
mount: wrong fs type, bad option, bad superblock on /cgroup,
...

mount1
Fri Feb 13 14:08:34 CST 2009
umount: /mnt: not mounted
mount: wrong fs type, bad option, bad superblock on /cgroup,
...

mount1
Fri Feb 13 14:08:43 CST 2009
umount: /mnt: not mounted
mount: wrong fs type, bad option, bad superblock on /cgroup,
...