From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: Re: [PATCH 3/3] netfilter: ctnetlink: allow userspace to set labels Date: Tue, 27 Nov 2012 15:13:17 +0100 Message-ID: <20121127141317.GB9089@1984> References: <1352994915-3859-1-git-send-email-fw@strlen.de> <1352994915-3859-4-git-send-email-fw@strlen.de> <20121127111838.GA28064@1984> <20121127115000.GA14156@breakpoint.cc> <20121127123149.GA2351@1984> <20121127130904.GB14156@breakpoint.cc> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netfilter-devel To: Florian Westphal Return-path: Received: from mail.us.es ([193.147.175.20]:49706 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755715Ab2K0ON2 (ORCPT ); Tue, 27 Nov 2012 09:13:28 -0500 Content-Disposition: inline In-Reply-To: <20121127130904.GB14156@breakpoint.cc> Sender: netfilter-devel-owner@vger.kernel.org List-ID: On Tue, Nov 27, 2012 at 02:09:04PM +0100, Florian Westphal wrote: > Pablo Neira Ayuso wrote: > > > > For the update case, I think we'll have to iterate over the mask and > > > > use xchg to update words, thus, we avoid any interference ongoing bit > > > > testing. > > > > > > Could you elaborate? > > > Why is memcpy not good enough here? > > > > while updating the connlabel via memcpy, some test_bit on the > > connlabel may be already happening. I was suggesting some way to avoid > > racing with it. > > I don't understand why its racing. > > Is there a case where we update a word, and test_bit can return > "bit is set", even if the bit in the word is neither currently > set nor about to be set? > > If not, then I don't see the race; either the test happens > before we copied the word, or afterwards; regardless of copy vs. > xchg? I was thinking on the case in which we are setting bits via the connlabel extension and modifying this from ctnetlink at the same time. But I don't see any way to make it any better, I think your approach is fine for the update case.