Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756040AbZICRHh (ORCPT ); Thu, 3 Sep 2009 13:07:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755989AbZICRHg (ORCPT ); Thu, 3 Sep 2009 13:07:36 -0400 Received: from smtp2.ultrahosting.com ([74.213.174.253]:55009 "EHLO smtp.ultrahosting.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752640AbZICRHf (ORCPT ); Thu, 3 Sep 2009 13:07:35 -0400 Date: Thu, 3 Sep 2009 14:24:17 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@V090114053VZO-1 To: Eric Dumazet cc: Pekka Enberg , Zdenek Kabelac , Patrick McHardy , Robin Holt , Linux Kernel Mailing List , Jesper Dangaard Brouer , Linux Netdev List , Netfilter Developers , paulmck@linux.vnet.ibm.com Subject: Re: [PATCH] slub: fix slab_pad_check() In-Reply-To: <4A9FDA72.8060001@gmail.com> Message-ID: References: <4A87CE60.4020506@gmail.com> <4A896324.3040104@trash.net> <4A9EEF07.5070800@gmail.com> <4A9F1620.2080105@gmail.com> <84144f020909022331x2b275aa5n428f88670e0ae8bc@mail.gmail.com> <4A9F7283.1090306@gmail.com> <4A9FCDC6.3060003@gmail.com> <4A9FDA72.8060001@gmail.com> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2324 Lines: 60 On Thu, 3 Sep 2009, Eric Dumazet wrote: > Point is we cannot deal with RCU quietness before disposing the slab cache, > (if SLAB_DESTROY_BY_RCU was set on the cache) since this disposing *will* > make call_rcu() calls when a full slab is freed/purged. There is no need to do call_rcu calls for frees at that point since objects are no longer in use. We could simply disable SLAB_DESTROY_BY_RCU for the final clearing of caches. > And when RCU grace period is elapsed, the callback *will* need access to > the cache we want to dismantle. Better to not have kfreed()/poisoned it... But going through the RCU period is pointless since no user of the cache remains. > I believe you mix two RCU uses here. > > 1) The one we all know, is use normal caches (!SLAB_DESTROY_BY_RCU) > (or kmalloc()), and use call_rcu(... kfree_something) > > In this case, you are 100% right that the subsystem itself has > to call rcu_barrier() (or respect whatever self-synchro) itself, > before calling kmem_cache_destroy() > > 2) The SLAB_DESTROY_BY_RCU one. > > Part of cache dismantle needs to call rcu_barrier() itself. > Caller doesnt have to use rcu_barrier(). It would be a waste of time, > as kmem_cache_destroy() will refill rcu wait queues with its own stuff. The dismantling does not need RCU since there are no operations on the objects in progress. So simply switch DESTROY_BY_RCU off for close. --- mm/slub.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: linux-2.6/mm/slub.c =================================================================== --- linux-2.6.orig/mm/slub.c 2009-09-03 10:14:51.000000000 -0500 +++ linux-2.6/mm/slub.c 2009-09-03 10:18:32.000000000 -0500 @@ -2594,9 +2594,9 @@ static inline int kmem_cache_close(struc */ void kmem_cache_destroy(struct kmem_cache *s) { - if (s->flags & SLAB_DESTROY_BY_RCU) - rcu_barrier(); down_write(&slub_lock); + /* Stop deferring frees so that we can immediately free structures */ + s->flags &= ~SLAB_DESTROY_BY_RCU; s->refcount--; if (!s->refcount) { list_del(&s->list); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/