linux-kernel - Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no

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Message-ID: <4993BD5D.2020707@cn.fujitsu.com>
Date:	Thu, 12 Feb 2009 14:10:37 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	containers@...ts.osdl.org, Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [cgroup or VFS ?] WARNING: at	fs/namespace.c:636	mntput_no_expire+0xac/0xf2()

Li Zefan wrote:
> Al Viro wrote:
>> On Mon, Feb 09, 2009 at 12:40:46AM -0800, Andrew Morton wrote:
>>>> Thread 1:
>>>>   for ((; ;))
>>>>   {
>>>>       mount -t cgroup -o cpuset xxx /mnt > /dev/null 2>&1
>>>>       mkdir /mnt/0 > /dev/null 2>&1
>>>>       rmdir /mnt/0 > /dev/null 2>&1
>>>>       umount /mnt > /dev/null 2>&1
>>>>   }
>>>>
>>>> Thread 2:
>>>>   {
>>>>       mount -t cpuset xxx /mnt > /dev/null 2>&1
>>>>       umount /mnt > /dev/null 2>&1
>>>>   }
>> How cute...  Same mountpoint in both, so these mount(2) will sometimes
>> fail (cgroup picks the same sb on the same options, AFAICS) and fail
>> silently due to these redirects...
>>
>> That's a lovely way to stress-test a large part of ro-bind stuff *and*
>> umount()-related code.  Could you do C equivalent of the above (just
>> the same syscalls in loop, nothing fancier) and do time-stamped strace?
>>
> 
> Sure, I'll write a C version and try to reproduce the warning.
> 

Unfortunately, the C equivalent can't reproduce the warning, I've run the
test for the whole night. :( While using the script, often I can trigger
the warning in several mins.

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