Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753164Ab0KLHIl (ORCPT ); Fri, 12 Nov 2010 02:08:41 -0500 Received: from mail-vw0-f46.google.com ([209.85.212.46]:45174 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750936Ab0KLHIk (ORCPT ); Fri, 12 Nov 2010 02:08:40 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=IRoXDTKQ+IWQl5DbX/AcKyv71ra0Oec4a4f4TRe7O55Y+q4VFoYJgTJUn+Hh1wqZYt iSmidJu/5h0pv5Tl94rDP+Rcqb6dK/Yp3j5mW6Pnzi+kuNFNCprtjPvuPCNEk8PSAC3I RXm/fpRTWCjVnW5nznawWqg5EINYsXng1RJWI= Date: Fri, 12 Nov 2010 15:13:23 +0800 From: =?utf-8?Q?Am=C3=A9rico?= Wang To: Cypher Wu Cc: Eric Dumazet , linux-kernel@vger.kernel.org, netdev Subject: Re: Kernel rwlock design, Multicore and IGMP Message-ID: <20101112071323.GB5660@cr0.nay.redhat.com> References: <1289489007.17691.1310.camel@edumazet-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1654 Lines: 38 On Fri, Nov 12, 2010 at 11:32:59AM +0800, Cypher Wu wrote: >On Thu, Nov 11, 2010 at 11:23 PM, Eric Dumazet wrote: >> Le jeudi 11 novembre 2010 à 21:49 +0800, Cypher Wu a écrit : >> >> Hi >> >> CC netdev, since you ask questions about network stuff _and_ rwlock >> >> >>> I'm using TILEPro and its rwlock in kernel is a liitle different than >>> other platforms. It have a priority for write lock that when tried it >>> will block the following read lock even if read lock is hold by >>> others. Its code can be read in Linux Kernel 2.6.36 in >>> arch/tile/lib/spinlock_32.c. >> >> This seems a bug to me. >> >> read_lock() can be nested. We used such a schem in the past in iptables >> (it can re-enter itself), >> and we used instead a spinlock(), but with many discussions with lkml >> and Linus himself if I remember well. >> >It seems not a problem that read_lock() can be nested or not since >rwlock doesn't have 'owner', it's just that should we give >write_lock() a priority than read_lock() since if there have a lot >read_lock()s then they'll starve write_lock(). >We should work out a well defined behavior so all the >platform-dependent raw_rwlock has to design under that principle. It is a known weakness of rwlock, it is designed like that. :) The solution is to use RCU or seqlock, but I don't think seqlock is proper for this case you described. So, try RCU lock. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/