Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758131Ab2FFUAH (ORCPT ); Wed, 6 Jun 2012 16:00:07 -0400 Received: from mail-ee0-f46.google.com ([74.125.83.46]:64762 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751257Ab2FFUAE (ORCPT ); Wed, 6 Jun 2012 16:00:04 -0400 Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches From: Eric Dumazet To: "Michael S. Tsirkin" Cc: Jason Wang , netdev@vger.kernel.org, rusty@rustcorp.com.au, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Stephen Hemminger In-Reply-To: <20120606165754.GA19357@redhat.com> References: <1338971724.2760.3913.camel@edumazet-glaptop> <1338972341.2760.3944.camel@edumazet-glaptop> <20120606111357.GA15070@redhat.com> <1338988210.2760.4485.camel@edumazet-glaptop> <20120606144941.GA17092@redhat.com> <1338995944.26966.6.camel@edumazet-glaptop> <20120606165754.GA19357@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 06 Jun 2012 22:00:00 +0200 Message-ID: <1339012800.26966.53.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 729 Lines: 21 On Wed, 2012-06-06 at 19:57 +0300, Michael S. Tsirkin wrote: > So for virtio since all counters get incremented from bh we can > ensure they are read atomically, simply but reading them > from the correct CPU with bh disabled. > And then we don't need u64_stats_sync at all. > Really ? How are you going to read 64bit stats from foreign cpus on 32bit arches, without additional cost in fast path ? You should read include/linux/u64_stats_sync.h to fully understand the issues. -- 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/