From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH v3 nf-next 1/2] netfilter: x_tables: wait until old table isn't used anymore Date: Wed, 11 Oct 2017 08:09:56 -0700 Message-ID: References: <20171011142607.15026-1-fw@strlen.de> <20171011142607.15026-2-fw@strlen.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: netfilter-devel@vger.kernel.org, Dan Williams To: Florian Westphal Return-path: Received: from mail-qt0-f172.google.com ([209.85.216.172]:46955 "EHLO mail-qt0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757193AbdJKPJ6 (ORCPT ); Wed, 11 Oct 2017 11:09:58 -0400 Received: by mail-qt0-f172.google.com with SMTP id 1so6146201qtn.3 for ; Wed, 11 Oct 2017 08:09:58 -0700 (PDT) In-Reply-To: <20171011142607.15026-2-fw@strlen.de> Sender: netfilter-devel-owner@vger.kernel.org List-ID: On Wed, Oct 11, 2017 at 7:26 AM, Florian Westphal wrote: > xt_replace_table relies on table replacement counter retrieval (which > uses xt_recseq to synchronize pcpu counters). > > This is fine, however with large rule set get_counters() can take > a very long time -- it needs to synchronize all counters because > it has to assume concurrent modifications can occur. > > Make xt_replace_table synchronize by itself by waiting until all cpus > had an even seqcount. > > This allows a followup patch to copy the counters of the old ruleset > without any synchonization after xt_replace_table has completed. > > Cc: Dan Williams > Cc: Eric Dumazet > Signed-off-by: Florian Westphal > --- > v3: check for 'seq is uneven' OR 'has changed' since > last check. Its fine if seq is uneven iff its a different > sequence number than the initial one. > > v2: fix Erics email address > net/netfilter/x_tables.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > Reviewed-by: Eric Dumazet But it seems we need an extra smp_wmb() after smp_wmb(); table->private = newinfo; + smp_wmb(); Otherwise we have no guarantee other cpus actually see the new ->private value.