linux-kernel - Re: [PATCH] slub: make sysfs file removal asynchronous

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Message-ID: <20170620220011.GJ21326@htj.duckdns.org>
Date:   Tue, 20 Jun 2017 18:00:11 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] slub: make sysfs file removal asynchronous

On Tue, Jun 20, 2017 at 02:58:14PM -0700, Andrew Morton wrote:
> On Tue, 20 Jun 2017 16:45:12 -0400 Tejun Heo <tj@...nel.org> wrote:
> 
> > bf5eb3de3847 ("slub: separate out sysfs_slab_release() from
> > sysfs_slab_remove()") made slub sysfs file removals synchronous to
> > kmem_cache shutdown.  Unfortunately, this created a possible ABBA
> > deadlock between slab_mutex and sysfs draining mechanism triggering
> > the following lockdep warning.
> > 
> > ...
> >
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Reported-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > Tested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > Fixes: bf5eb3de3847 ("slub: separate out sysfs_slab_release() from sysfs_slab_remove()")
> 
> Do you think we should add cc:stable [4.11+]?

I think we'd risk more by backporting it through -stable than keeping
the bug there.  The bug is very difficult to hit.  Writing to a slub
sysfs file has to race against kmem_cache destruction and AFAICS all
slub sysfs files are for debugging.

Thanks.

-- 
tejun