Re: [ 004/120] slab: fix the DEADLOCK issue on l3 alien lock

Greg Kroah-Hartman
2012-10-18T17:14:21Z

On Thu, Oct 18, 2012 at 09:20:20AM -0400, Steven Rostedt wrote:
> On Thu, Oct 11, 2012 at 09:59:16AM +0900, Greg Kroah-Hartman wrote:
> > 3.4-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Michael Wang <wangyun@linux.vnet.ibm.com>
> >
> > commit 947ca1856a7e60aa6d20536785e6a42dff25aa6e upstream.
> >
> > DEADLOCK will be report while running a kernel with NUMA and LOCKDEP enabled,
> > the process of this fake report is:
> >
> > kmem_cache_free() //free obj in cachep
> > -> cache_free_alien() //acquire cachep's l3 alien lock
> > -> __drain_alien_cache()
> > -> free_block()
> > -> slab_destroy()
> > -> kmem_cache_free() //free slab in cachep->slabp_cache
> > -> cache_free_alien() //acquire cachep->slabp_cache's l3 alien lock
> >
> > Since the cachep and cachep->slabp_cache's l3 alien are in the same lock class,
> > fake report generated.
> >
> > This should not happen since we already have init_lock_keys() which will
> > reassign the lock class for both l3 list and l3 alien.
> >
> > However, init_lock_keys() was invoked at a wrong position which is before we
> > invoke enable_cpucache() on each cache.
> >
> > Since until set slab_state to be FULL, we won't invoke enable_cpucache()
> > on caches to build their l3 alien while creating them, so although we invoked
> > init_lock_keys(), the l3 alien lock class won't change since we don't have
> > them until invoked enable_cpucache() later.
> >
> > This patch will invoke init_lock_keys() after we done enable_cpucache()
> > instead of before to avoid the fake DEADLOCK report.
> >
> > Michael traced the problem back to a commit in release 3.0.0:
>
> I don't see this fix in the last 3.0 stable release. Shouldn't it go
> there too?

As-is, it doesn't apply at all. If someone provides me a backport, I'll
be glad to apply it there.

thanks,

greg k-h