From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752958Ab3KTNeM (ORCPT ); Wed, 20 Nov 2013 08:34:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39099 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750796Ab3KTNeJ (ORCPT ); Wed, 20 Nov 2013 08:34:09 -0500 Date: Wed, 20 Nov 2013 15:37:07 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Michael Dalton , Eric Dumazet Subject: Re: [PATCH net 2/3] virtio-net: fix num calculation on frag skb allocation failure Message-ID: <20131120133707.GA8523@redhat.com> References: <1384938447-3775-1-git-send-email-jasowang@redhat.com> <1384938447-3775-2-git-send-email-jasowang@redhat.com> <20131120103729.GG19341@redhat.com> <734327384.27426189.1384949330819.JavaMail.root@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <734327384.27426189.1384949330819.JavaMail.root@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 20, 2013 at 07:08:50AM -0500, Jason Wang wrote: > > > ----- 原始邮件 ----- > > On Wed, Nov 20, 2013 at 05:07:26PM +0800, Jason Wang wrote: > > > We need decrease the rq->num after we can get a buf through > > > virtqueue_get_buf() even if we could not allocate frag skb. Otherwise, the > > > refill routine won't be triggered under heavy memory stress since the > > > driver may > > > still think there's enough room. > > > > > > This bug was introduced by commit 2613af0ed18a11d5c566a81f9a6510b73180660a > > > (virtio_net: migrate mergeable rx buffers to page frag allocators). > > > > > > Cc: Rusty Russell > > > Cc: Michael S. Tsirkin > > > Cc: Michael Dalton > > > Cc: Eric Dumazet > > > Signed-off-by: Jason Wang > > > > So let's wrap virtqueue_get_buf to make sure we get it right? > > > > Ok. good idea. So I did this (below) but the compiler is not smart enough to avoid two branches on data path. So I'm not sure anymore: with my patch it's pretty clear how the code works. Signed-off-by: Michael S. Tsirkin but I don't think we need to apply this. diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 11d9cc9..1cc2e43 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -296,6 +296,14 @@ static struct sk_buff *page_to_skb(struct receive_queue *rq, return skb; } +static void *rq_get_buf(struct receive_queue *rq, unsigned int *len) +{ + void *buf = virtqueue_get_buf(rq->vq, len); + if (buf) + rq->num--; + return buf; +} + static struct sk_buff *receive_mergeable(struct net_device *dev, struct receive_queue *rq, void *buf, @@ -315,7 +323,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, while (--num_buf) { int num_skb_frags; - buf = virtqueue_get_buf(rq->vq, &len); + buf = rq_get_buf(rq, &len); if (unlikely(!buf)) { pr_debug("%s: rx error: %d buffers out of %d missing\n", dev->name, num_buf, hdr->mhdr.num_buffers); @@ -329,7 +337,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, } page = virt_to_head_page(buf); - --rq->num; num_skb_frags = skb_shinfo(curr_skb)->nr_frags; if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) { @@ -370,7 +377,7 @@ err_buf: dev->stats.rx_dropped++; dev_kfree_skb(head_skb); while (--num_buf) { - buf = virtqueue_get_buf(rq->vq, &len); + buf = rq_get_buf(rq, &len); if (unlikely(!buf)) { pr_debug("%s: rx error: %d buffers missing\n", dev->name, num_buf); @@ -379,7 +386,6 @@ err_buf: } page = virt_to_head_page(buf); put_page(page); - --rq->num; } return NULL; } @@ -675,9 +681,8 @@ static int virtnet_poll(struct napi_struct *napi, int budget) again: while (received < budget && - (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) { + (buf = rq_get_buf(rq, &len)) != NULL) { receive_buf(rq, buf, len); - --rq->num; received++; }