linux-kernel - Re: cgroup: rmdir() does not complete

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Message-Id: <20100902084200.e9b773cf.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 2 Sep 2010 08:42:00 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mark Hills <mark@...o.org.uk>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com
Subject: Re: cgroup: rmdir() does not complete

On Wed, 1 Sep 2010 12:10:23 +0100 (BST)
Mark Hills <mark@...o.org.uk> wrote:

> On Fri, 27 Aug 2010, KAMEZAWA Hiroyuki wrote:
> 
> > On Fri, 27 Aug 2010 12:39:48 +0900
> > Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > 
> > > On Fri, 27 Aug 2010 11:35:06 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > > 
> > > > On Fri, 27 Aug 2010 09:56:39 +0900
> > > > Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > > > 
> > > > > > Or is it likely to be some other cause, and how best to find it?
> > > > > > 
> > > > > What cgroup subsystem did you mount where the directory existed you tried
> > > > > to rmdir() first ?
> > > > > If you mounted several subsystems on the same hierarchy, can you mount them
> > > > > separately to narrow down the cause ?
> > > > > 
> > > > 
> > > > It seems I can reproduce the issue on mmotm-0811, too.
> > > > 
> > > > try this.
> > > > 
> > > > Here, memory cgroup is mounted at /cgroups.
> > > > ==
> > > > #!/bin/bash -x
> > > > 
> > > > while sleep 1; do
> > > >         date
> > > >         mkdir /cgroups/test
> > > >         echo 0 > /cgroups/test/tasks
> > > >         echo 300M > /cgroups/test/memory.limit_in_bytes
> > > >         cat /proc/self/cgroup
> > > >         dd if=/dev/zero of=./tmpfile bs=4096 count=100000
> > > >         echo 0 > /cgroups/tasks
> > > >         cat /proc/self/cgroup
> > > >         rmdir /cgroups/test
> > > >         rm ./tmpfile
> > > > done
> > > > ==
> > > > 
> > > > hangs at rmdir. I'm no investigating force_empty.
> > > > 
> > > Thank you very much for your information.
> > > 
> > > Some questions.
> > > 
> > > Is "tmpfile" created on a normal filesystem(e.g. ext3) or tmpfs ?
> > on ext4.
> > 
> > > And, how long does it likely to take to cause this problem ?
> > 
> > very soon. 10-20 loop.
> 
> I repeated the test above, but did not see a problem after many hundreds 
> of loops.
> 
> My test was with the same kernel from my original bug report (Fedora 
> 2.6.33.6-147), using memory cgroup only and ext4 filesystem.
> 
> So it is possible we are experiencing different bugs with similar 
> symptoms.
> 

Thank you for confirming.
But hmm...it's curious who holds mutex and what happens.

-Kame

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