linux-kernel - Re: lockdep trace from prepare_bprm

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Message-ID: <20130307193342.GA3209@htj.dyndns.org>
Date:	Thu, 7 Mar 2013 11:33:42 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org
Subject: Re: lockdep trace from prepare_bprm_creds

On Thu, Mar 07, 2013 at 07:32:14PM +0100, Oleg Nesterov wrote:
> On 03/07, Tejun Heo wrote:
> >
> > On Thu, Mar 07, 2013 at 10:01:39AM -0800, Tejun Heo wrote:
> > >
> > > Another possibility is moving cgroup_lock outside threadgroup_lock(),
> > > which was impossible before because of cgroup_lock abuses in specific
> > > controller implementations but most of that have been updated and we
> > > should now be pretty close to being able to make cgroup_lock outer to
> > > most other locks.  Appending a completely untested patch below.
> >
> > This probably doesn't help as the dependency involves i_mutex.
> 
> Confused... why?

Maybe I'm confused.  We still have i_mutex -> cgroup_lock from the
mount path.  The original deadlock was cred_mutex -> i_mutex
vs. i_mutex -> cgroup_mutex -> cred_mutex.  The patch changes the
latter to i_mutex -> cgroup_mutex and cred_mutex -> cgroup_mutex.
Gosh, it's confusing, yeah, we might be okay.

-- 
tejun
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