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 15:10:10 +0200 Message-ID: <1338988210.2760.4485.camel@edumazet-glaptop> References: <1338971724.2760.3913.camel@edumazet-glaptop> <1338972341.2760.3944.camel@edumazet-glaptop> <20120606111357.GA15070@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: <20120606111357.GA15070@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 14:13 +0300, Michael S. Tsirkin wrote: > We currently do all stats either on napi callback or from > start_xmit callback. > This makes them safe, yes? Hmm, then _bh() variant is needed in virtnet_stats(), as explained in include/linux/u64_stats_sync.h section 6) * 6) If counter might be written by an interrupt, readers should block interrupts. * (On UP, there is no seqcount_t protection, a reader allowing interrupts could * read partial values) Yes, its tricky... diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 5214b1e..705aaa7 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -703,12 +703,12 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev, u64 tpackets, tbytes, rpackets, rbytes; do { - start = u64_stats_fetch_begin(&stats->syncp); + start = u64_stats_fetch_begin_bh(&stats->syncp); tpackets = stats->tx_packets; tbytes = stats->tx_bytes; rpackets = stats->rx_packets; rbytes = stats->rx_bytes; - } while (u64_stats_fetch_retry(&stats->syncp, start)); + } while (u64_stats_fetch_retry_bh(&stats->syncp, start)); tot->rx_packets += rpackets; tot->tx_packets += tpackets;