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 <rusty@xxxxxxxxxxxxxxx> > > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > Cc: Michael Dalton <mwdalton@xxxxxxxxxx> > > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > > > 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 <mst@xxxxxxxxxx> 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++; } _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization