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

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Message-ID: <20090209093414.GU28946@ZenIV.linux.org.uk>
Date:	Mon, 9 Feb 2009 09:34:14 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Menage <menage@...gle.com>, containers@...ts.osdl.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [cgroup or VFS ?]  WARNING: at fs/namespace.c:636
	mntput_no_expire+0xac/0xf2()

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?
--
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