From: Vlad Yasevich Subject: Re: [PATCH 4/5] sctp: protocol.c call rcu_barrier() on unload. Date: Tue, 09 Jun 2009 12:26:25 -0400 Message-ID: <4A2E8D31.1030307@hp.com> References: <20090608130959.10052.54590.stgit@localhost> <20090608131143.10052.96470.stgit@localhost> <20090608162227.GE6961@linux.vnet.ibm.com> <4A2E8357.80509@hp.com> <20090609155011.GD6789@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Jesper Dangaard Brouer , "David S. Miller" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, urs.thuermann-l29pVbxQd1IUtdQbppsyvg@public.gmane.org, oliver.hartkopp-l29pVbxQd1IUtdQbppsyvg@public.gmane.org, wg-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org, sri@us.ibm.com, linux-sctp@vger.kernel.org, Trond.Myklebust@netapp.com, linux-nfs@vger.kernel.org, netfilter-devel@vger.kernel.org To: paulmck@linux.vnet.ibm.com Return-path: Received: from g5t0006.atlanta.hp.com ([15.192.0.43]:3818 "EHLO g5t0006.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753338AbZFIQ0Z (ORCPT ); Tue, 9 Jun 2009 12:26:25 -0400 In-Reply-To: <20090609155011.GD6789@linux.vnet.ibm.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: Paul E. McKenney wrote: > On Tue, Jun 09, 2009 at 11:44:23AM -0400, Vlad Yasevich wrote: >> Paul E. McKenney wrote: >>> On Mon, Jun 08, 2009 at 03:11:43PM +0200, Jesper Dangaard Brouer wrote: >>>> On module unload call rcu_barrier(), this is needed as synchronize_rcu() >>>> is not strong enough. The kmem_cache_destroy() does invoke >>>> synchronize_rcu() but it does not provide same protection. >>> Good, looks like sctp_v4_del_protocol() invokes call_rcu(), which the >>> rcu_barrier() would then wait for. And it looks like sctp_v6_del_protocol() >>> does the same for IPv6. >>> >>> Reviewed_by: Paul E. McKenney >>> >>>> Signed-off-by: Jesper Dangaard Brouer >>>> --- >>>> >>>> net/sctp/protocol.c | 2 ++ >>>> 1 files changed, 2 insertions(+), 0 deletions(-) >>>> >>>> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c >>>> index cb2c50d..79cbd47 100644 >>>> --- a/net/sctp/protocol.c >>>> +++ b/net/sctp/protocol.c >>>> @@ -1370,6 +1370,8 @@ SCTP_STATIC __exit void sctp_exit(void) >>>> sctp_proc_exit(); >>>> cleanup_sctp_mibs(); >>>> >>>> + rcu_barrier(); /* Wait for completion of call_rcu()'s */ >>>> + >>>> kmem_cache_destroy(sctp_chunk_cachep); >>>> kmem_cache_destroy(sctp_bucket_cachep); >>>> } >> Shouldn't the rcu_barrier call be before sctp_free_local_addr_list()? > > Hmmm... What sequence of events would lead to a failure if > rcu_barrier() is after sctp_free_local_addr_list()? > > Thanx, Paul > I thought that the notifier could could potentially execute at the same time as the unregister(), but I see that's protected. So, I guess it doesn't really matter then where the barrier is. Acked-by: Vlad Yasevich -vlad