From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick McHardy Subject: Re: [PATCH] netfilter: add locking for counters zeroing Date: Wed, 24 Sep 2008 18:11:42 +0200 Message-ID: <48DA66BE.6090209@trash.net> References: <4884bd82.Dh41l9jJY8sI8ajg%ole@ans.pl> <48DA643C.5000702@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Krzysztof Piotr Oledzki , netfilter-devel@vger.kernel.org To: Jan Engelhardt Return-path: Received: from stinky.trash.net ([213.144.137.162]:41315 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751681AbYIXQLr (ORCPT ); Wed, 24 Sep 2008 12:11:47 -0400 In-Reply-To: Sender: netfilter-devel-owner@vger.kernel.org List-ID: Jan Engelhardt wrote: > On Wednesday 2008-09-24 12:01, Patrick McHardy wrote: >>> @@ -545,6 +545,7 @@ ctnetlink_dump_table(struct sk_buff *skb, struct >>> netlink_callback *cb) >>> u_int8_t l3proto = nfmsg->nfgen_family; >>> >>> rcu_read_lock(); >>> + spin_lock_bh(&nf_conntrack_lock); >> We only need the spinlock. I'm not so happy about taking it >> unconditionally even though we might not be zeroing the >> counters. Moving it in the inner loop will greatly increase >> the amount of locks/unlocks on the other hand. >> >> How about moving the inner loop to a new function and adding >> back the ctnetlink_dump_counterzero (or whatever it was called) >> function? It would take the spinlock, while normal dumping >> would only use rcu_read_lock(). > > Perhaps this might work? > > + if (cb->args[0] >= nf_conntrack_htable_size) { > + nf_ct_put(cb->args[1]); > + return skb->len; > + } I'm not sure what you're trying to fix here. Its a race between counter zeroing and changing them during packet processing. Any patch that doesn't include a spin_lock can't really fix the problem :)