Re: [PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem in sl[aou]b

Matt Mackall
2009-06-25T21:26:50Z

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@selenic.com>

Nick, you'll want to make sure you get this in SLQB.

> Reported-by: Jesper Dangaard Brouer <jdb@comx.dk>
> Signed-off-by: Paul E. McKenney <paulmck@linux.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) {

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