From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753928Ab3KTN5E (ORCPT ); Wed, 20 Nov 2013 08:57:04 -0500 Received: from mx4-phx2.redhat.com ([209.132.183.25]:59130 "EHLO mx4-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751971Ab3KTN5C convert rfc822-to-8bit (ORCPT ); Wed, 20 Nov 2013 08:57:02 -0500 Date: Wed, 20 Nov 2013 08:56:54 -0500 (EST) From: Jason Wang To: "Michael S. Tsirkin" Cc: rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Michael Dalton , Eric Dumazet Message-ID: <1382353279.27479040.1384955814610.JavaMail.root@redhat.com> In-Reply-To: <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> <20131120133707.GA8523@redhat.com> Subject: Re: [PATCH net 2/3] virtio-net: fix num calculation on frag skb allocation failure MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.5.82.11] X-Mailer: Zimbra 8.0.3_GA_5664 (ZimbraWebClient - GC31 (Win)/8.0.3_GA_5664) Thread-Topic: virtio-net: fix num calculation on frag skb allocation failure Thread-Index: cgqlu+a4lVAdjpkRe3SLlR25rxbCuw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- 原始邮件 ----- > 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. > True, another point is we'd better to handle both increasing and decreasing in the same way. We do not increase it in a helper. > 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++; > } > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >