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

[Steven Rostedt]

On Sat, 20 May 2017 06:16:45 -0700
Christoph Hellwig <hch@xxxxxxxxxxxxx> 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