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SubjectRe: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2()
On Mon, 09 Feb 2009 09:48:59 -0800
Dave Hansen <dave@linux.vnet.ibm.com> wrote:

> On Mon, 2009-02-09 at 09:34 +0000, 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?
>
> Could you also add a printk of what ->__mnt_writers was at the time of
> the WARN_ON()? That will hopefully at least tell us whether we're
> looking at a real leak or just a single missed mnt_want/drop_write().
> Also hopefully in which direction the thing is biased. With the mount
> not being around long I'm not horribly hopeful, but it can't hurt.

... we could just change the WARN_ON to a WARN().. which has printk
semantics ;)


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Arjan van de Ven Intel Open Source Technology Centre
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