From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches Date: Wed, 06 Jun 2012 22:00:00 +0200 Message-ID: <1339012800.26966.53.camel@edumazet-glaptop> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Stephen Hemminger To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20120606165754.GA19357@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org 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.