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Date: Mon, 09 Feb 2009 19:30:20 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: Al Viro <viro@ZenIV.linux.org.uk>
CC: Andrew Morton <akpm@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>, Paul Menage <menage@google.com>,
       containers@lists.osdl.org, Arjan van de Ven <arjan@infradead.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>
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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.