From: Patrick McHardy Subject: Re: [PATCH v2 10/10] nf_conntrack: Use rcu_barrier() and fix kmem_cache_create flags Date: Wed, 24 Jun 2009 15:58:32 +0200 Message-ID: <4A423108.60109@trash.net> References: <20090623150330.22490.87327.stgit@localhost> <20090623150444.22490.27931.stgit@localhost> <4A410185.3090706@trash.net> <1245834139.6695.31.camel@localhost.localdomain> <1245836409.6695.35.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , "Paul E. McKenney" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dougthompson@xmission.com, bluesmoke-devel@lists.sourceforge.net, axboe@kernel.dk, christine.caulfield@googlemail.com, Trond.Myklebust@netapp.com, linux-wireless@vger.kernel.org, johannes@sipsolutions.net, yoshfuji@linux-ipv6.org, shemminger@linux-foundation.org, linux-nfs@vger.kernel.org, bfields@fieldses.org, neilb@suse.de, linux-ext4@vger.kernel.org, tytso@mit.edu, adilger@sun.com, netfilter-devel@vger.kernel.org To: jdb@comx.dk Return-path: Received: from stinky.trash.net ([213.144.137.162]:47283 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752498AbZFXN6e (ORCPT ); Wed, 24 Jun 2009 09:58:34 -0400 In-Reply-To: <1245836409.6695.35.camel@localhost.localdomain> Sender: linux-ext4-owner@vger.kernel.org List-ID: Jesper Dangaard Brouer wrote: > Adjusting SLAB_DESTROY_BY_RCU flags. > > kmem_cache_create("nf_conntrack", ...) does not need the > SLAB_DESTROY_BY_RCU flag. It does need it. We're using it instead of call_rcu() for conntracks. > But the > kmem_cache_create("nf_conntrack_expect", ...) should use the > SLAB_DESTROY_BY_RCU flag, because it uses a call_rcu() callback to > invoke kmem_cache_free(). No, using call_rcu() means we don't need SLAB_DESTROY_BY_RCU. Please see the note in include/linux/slab.h. > RCU barriers, rcu_barrier(), is inserted two places. > > In nf_conntrack_expect.c nf_conntrack_expect_fini() before the > kmem_cache_destroy(), even though the use of the SLAB_DESTROY_BY_RCU > flag, because slub does not (currently) handle rcu sync correctly. I think that should be fixed in slub then. > And in nf_conntrack_extend.c nf_ct_extend_unregister(), inorder to > wait for completion of callbacks to __nf_ct_ext_free_rcu(), which is > invoked by __nf_ct_ext_add(). It might be more efficient to call > rcu_barrier() in nf_conntrack_core.c nf_conntrack_cleanup_net(), but > thats make it more difficult to read the code (as the callback code > in located in nf_conntrack_extend.c). This one looks fine. > diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c > index 5f72b94..438ce84 100644 > --- a/net/netfilter/nf_conntrack_core.c > +++ b/net/netfilter/nf_conntrack_core.c > @@ -1242,7 +1242,7 @@ static int nf_conntrack_init_init_net(void) > > nf_conntrack_cachep = kmem_cache_create("nf_conntrack", > sizeof(struct nf_conn), > - 0, SLAB_DESTROY_BY_RCU, NULL); > + 0, 0, NULL); > if (!nf_conntrack_cachep) { > printk(KERN_ERR "Unable to create nf_conn slab cache\n"); > ret = -ENOMEM; > diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c > index afde8f9..56227c2 100644 > --- a/net/netfilter/nf_conntrack_expect.c > +++ b/net/netfilter/nf_conntrack_expect.c > @@ -593,7 +593,7 @@ int nf_conntrack_expect_init(struct net *net) > if (net_eq(net, &init_net)) { > nf_ct_expect_cachep = kmem_cache_create("nf_conntrack_expect", > sizeof(struct nf_conntrack_expect), > - 0, 0, NULL); > + 0, SLAB_DESTROY_BY_RCU, NULL); > if (!nf_ct_expect_cachep) > goto err2; > } > @@ -617,8 +617,15 @@ err1: > void nf_conntrack_expect_fini(struct net *net) > { > exp_proc_remove(net); > - if (net_eq(net, &init_net)) > + if (net_eq(net, &init_net)) { > + /* hawk@comx.dk 2009-06-24: The rcu_barrier() can be > + * removed once the sl*b allocators has been fixed > + * regarding handling the SLAB_DESTROY_BY_RCU flag > + * correctly. > + */ > + rcu_barrier(); /* Wait for call_rcu() before destroy */ > kmem_cache_destroy(nf_ct_expect_cachep); > + } > nf_ct_free_hashtable(net->ct.expect_hash, net->ct.expect_vmalloc, > nf_ct_expect_hsize); > } > diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c > index 4b2c769..fef95be 100644 > --- a/net/netfilter/nf_conntrack_extend.c > +++ b/net/netfilter/nf_conntrack_extend.c > @@ -186,6 +186,6 @@ void nf_ct_extend_unregister(struct nf_ct_ext_type *type) > rcu_assign_pointer(nf_ct_ext_types[type->id], NULL); > update_alloc_size(type); > mutex_unlock(&nf_ct_ext_type_mutex); > - synchronize_rcu(); > + rcu_barrier(); /* Wait for completion of call_rcu()'s */ > } > EXPORT_SYMBOL_GPL(nf_ct_extend_unregister); >