From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] ipv6: prevent fib6_run_gc() contention Date: Tue, 11 Jun 2013 14:22:29 -0700 (PDT) Message-ID: <20130611.142229.497972115797274443.davem@davemloft.net> References: <20130611100718.GA7581@unicorn.suse.cz> <20130611.130114.764345999553478927.davem@davemloft.net> <20130611204912.GA1255@lion.mk-sys.cz> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, kuznet@ms2.inr.ac.ru, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net To: mkubecek@suse.cz Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:46236 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756048Ab3FKVWc (ORCPT ); Tue, 11 Jun 2013 17:22:32 -0400 In-Reply-To: <20130611204912.GA1255@lion.mk-sys.cz> Sender: netdev-owner@vger.kernel.org List-ID: From: Michal Kubecek Date: Tue, 11 Jun 2013 22:49:12 +0200 > On Tue, Jun 11, 2013 at 01:01:14PM -0700, David Miller wrote: >> From: Michal Kubecek >> Date: Tue, 11 Jun 2013 12:07:18 +0200 >> >> > On Mon, Jun 10, 2013 at 02:26:42PM -0700, David Miller wrote: >> >> >> >> It seems to me that it would be much simpler to simply update >> >> ip6_rt_last_gc first, that way the other threads would elide the GC >> >> call. >> > >> > That was my original idea but I was afraid that while the remaining >> > window in ip6_dst_gc() would be very short and probably safe, we could >> > still run into problem if fib6_gc_lock was locked by some other caller >> > of fib6_run_gc() which doesn't update net->ipv6.ip6_rt_last_gc, >> > especially via a timer. >> >> Why don't you simply try it and find out? > > I don't have the system where the issue was observed at hand. I'll have > to ask the customer who reported it to run the test so that it may take > some time. Please also take care of the issue Eric mentioned, in that some GC calls erroneously do not update the last GC timestamp.