linux-kernel - Re: [PATCH] slub/memcg: Cure the brainless abuse of sysfs attributes

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Date:   Sat, 20 May 2017 10:25:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] slub/memcg: Cure the brainless abuse of sysfs
 attributes

On Sat, 20 May 2017 06:16:45 -0700
Christoph Hellwig <hch@...radead.org> wrote:

> On Sat, May 20, 2017 at 12:52:03PM +0200, Thomas Gleixner wrote:
> > This should be rewritten proper by adding a propagate() callback to those
> > slub_attributes which must be propagated and avoid that insane conversion
> > to and from ASCII
> 
> Exactly..
> 
> >, but that's too large for a hot fix.
> 
> What made this such a hot fix?  Looks like this crap has been in
> for quite a while.

It can cause a deadlock with get_online_cpus() that has been uncovered
by recent cpu hotplug and lockdep changes that Thomas and Peter have
been doing.

[  102.567308]  Possible unsafe locking scenario:
[  102.567308] 
[  102.574846]        CPU0                    CPU1
[  102.580148]        ----                    ----
[  102.585421]   lock(cpu_hotplug.lock);
[  102.589808]                                lock(slab_mutex);
[  102.596166]                                lock(cpu_hotplug.lock);
[  102.603028]   lock(slab_mutex);
[  102.606846] 
[  102.606846]  *** DEADLOCK ***

-- Steve