linux-kernel - Re: lockdep trace from prepare_bprm

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Message-ID: <20130309032936.GT14556@mtj.dyndns.org>
Date:	Fri, 8 Mar 2013 19:29:36 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	cgroups@...r.kernel.org
Subject: Re: lockdep trace from prepare_bprm_creds

Hello, Li.

On Sat, Mar 09, 2013 at 10:11:51AM +0800, Li Zefan wrote:
> On 2013/3/8 3:38, Tejun Heo wrote:
> > On Thu, Mar 07, 2013 at 08:12:42PM +0100, Oleg Nesterov wrote:
> >> Well yes, I agree. I think that perfomance-wise threadgroup_change_begin()
> >> in de_thread() is fine, and perhaps it is even more clean because we are
> >> going to do the thread-group change. The scope of cred_guard_mutex is huge,
> >> it doesn't look very nice in threadgroup_lock().
> >>
> >> But we should avoid the cgroup-specific hooks as much as possible, so I
> >> like your patch more.
> > 
> > I don't really mind how it's done but while my approach seems to limit
> > itself to cgroup proper, threadgroup locking is actually more invasive
> > by meddling with cred_mutex.  As you said, yours is the cleaner and
> > probably more permanent one here.
> > 
> 
> Agreed.
> 
> Now we need that patch to be resent with SOB and proper changelog.

Now that I think more about it, I think I want both patches.  It is
bothering that threadgroup lock is nested inside cgroup_lock.  It
always has.  I just couldn't do anything about that until recently.
Li, can you be persuaded into getting the lock reordering patch into a
useable shape?  :)

Thanks.

-- 
tejun
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