linux-kernel - Re: [PATCH RFC] fix RCU-callback-after-kmem_cache

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Date:	Thu, 25 Jun 2009 15:08:37 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cl@...ux-foundation.org, penberg@...helsinki.fi, jdb@...x.dk,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem
	in sl[aou]b

On Thu, Jun 25, 2009 at 04:27:19PM -0500, Matt Mackall wrote:
> On Thu, 2009-06-25 at 12:31 -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > Jesper noted that kmem_cache_destroy() invokes synchronize_rcu() rather
> > than rcu_barrier() in the SLAB_DESTROY_BY_RCU case, which could result
> > in RCU callbacks accessing a kmem_cache after it had been destroyed.
> > 
> > The following untested (might not even compile) patch proposes a fix.
> 
> Acked-by: Matt Mackall <mpm@...enic.com>
> 
> Nick, you'll want to make sure you get this in SLQB.
> 
> > Reported-by: Jesper Dangaard Brouer <jdb@...x.dk>

And I seem to have blown Jesper's email address (apologies, Jesper!), so:

Reported-by: Jesper Dangaard Brouer <hawk@...x.dk>

> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> > 
> >  slab.c |    2 +-
> >  slob.c |    2 ++
> >  slub.c |    2 ++
> >  3 files changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/slab.c b/mm/slab.c
> > index e74a16e..5241b65 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -2547,7 +2547,7 @@ void kmem_cache_destroy(struct kmem_cache *cachep)
> >  	}
> >  
> >  	if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU))
> > -		synchronize_rcu();
> > +		rcu_barrier();
> >  
> >  	__kmem_cache_destroy(cachep);
> >  	mutex_unlock(&cache_chain_mutex);
> > diff --git a/mm/slob.c b/mm/slob.c
> > index c78742d..9641da3 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -595,6 +595,8 @@ EXPORT_SYMBOL(kmem_cache_create);
> >  void kmem_cache_destroy(struct kmem_cache *c)
> >  {
> >  	kmemleak_free(c);
> > +	if (c->flags & SLAB_DESTROY_BY_RCU)
> > +		rcu_barrier();
> >  	slob_free(c, sizeof(struct kmem_cache));
> >  }
> >  EXPORT_SYMBOL(kmem_cache_destroy);
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 819f056..a9201d8 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2595,6 +2595,8 @@ static inline int kmem_cache_close(struct kmem_cache *s)
> >   */
> >  void kmem_cache_destroy(struct kmem_cache *s)
> >  {
> > +	if (s->flags & SLAB_DESTROY_BY_RCU)
> > +		rcu_barrier();
> >  	down_write(&slub_lock);
> >  	s->refcount--;
> >  	if (!s->refcount) {
> 
> -- 
> http://selenic.com : development and support for Mercurial and Linux
> 
> 
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