Re: [PATCH] slub: make sysfs file removal asynchronous

[Tejun Heo]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Reported-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > Tested-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > 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