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Date: Wed, 20 Nov 2013 08:54:02 -0500 (EST)
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Michael Dalton <mwdalton@...gle.com>,
Eric Dumazet <edumazet@...gle.com>, Shirley Ma <xma@...ibm.com>
Subject: Re: [PATCH RFC] virtio_net: fix error handling for mergeable
buffers
----- 原始邮件 -----
> On Wed, Nov 20, 2013 at 05:07:25PM +0800, Jason Wang wrote:
> > When mergeable buffer were used, we only put the first page buf leave the
> > rest
> > of buffers in the virt queue. This will cause the driver could not get the
> > correct head buffer any more. Fix this by dropping the rest of buffers for
> > this
> > packet.
> >
> > The bug was introduced by commit 9ab86bbcf8be755256f0a5e994e0b38af6b4d399
> > (virtio_net: Defer skb allocation in receive path).
> >
> > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > Cc: Michael S. Tsirkin <mst@...hat.com>
> > Cc: Michael Dalton <mwdalton@...gle.com>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: Shirley Ma <xma@...ibm.com>
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
>
> Just to clarify my previous comment: it was not about the
> idea of adding drop_mergeable_buffer - rather, I think that
> adding knowledge about mergeable buffers into page_to_skb creates an
> ugly internal API.
>
> Let's move the call to page_to_skb within receive_mergeable instead:
> it's also nice that int offset = buf - page_address(page) logic
> is not spread around like it was.
>
> Also, it's not nice that we ignore length errors when we drop
> packets because of OOM.
>
> So I came up with the following - it seems to work but I didn't
> stress test yet.
I've no objection on this. But I've rather like my small and direct patch
to be applied to -net first. It has lower risk and was much more easier to
be backported to stable trees. Then we can do the re-factor like this in
net-next.
>
> commit ebffb3fe4335ffe07124e4518e76d6e05844fa18
> Author: Michael S. Tsirkin <mst@...hat.com>
> Date: Wed Nov 20 14:41:29 2013 +0200
>
> virtio_net: fix error handling for mergeable buffers
>
> Eric Dumazet noticed that if we encounter an error
> when processing a mergeable buffer, we don't
> dequeue all of the buffers from this packet,
> the result is almost sure to be loss of networking.
>
> Jason Wang noticed that we also leak a page and that we don't decrement
> the rq buf count, so we won't repost buffers (a resource leak).
>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael Dalton <mwdalton@...gle.com>
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 01f4eb5..42f6a1e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -296,41 +296,53 @@ static struct sk_buff *page_to_skb(struct receive_queue
> *rq,
> return skb;
> }
>
> -static int receive_mergeable(struct receive_queue *rq, struct sk_buff
> *head_skb)
> +static struct sk_buff *receive_mergeable(struct net_device *dev,
> + struct receive_queue *rq,
> + void *buf,
> + unsigned int len)
> {
> - struct skb_vnet_hdr *hdr = skb_vnet_hdr(head_skb);
> + struct skb_vnet_hdr *hdr = buf;
> + int num_buf = hdr->mhdr.num_buffers;
> + struct page *page = virt_to_head_page(buf);
> + int offset = buf - page_address(page);
> + struct sk_buff *head_skb = page_to_skb(rq, page, offset, len,
> + MAX_PACKET_LEN);
> struct sk_buff *curr_skb = head_skb;
> - char *buf;
> - struct page *page;
> - int num_buf, len, offset;
>
> - num_buf = hdr->mhdr.num_buffers;
> - while (--num_buf) {
> - int num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
> + if (unlikely(!curr_skb))
> + goto err_skb;
> +
> + while (--num_buf) {
> + int num_skb_frags;
> +
> buf = virtqueue_get_buf(rq->vq, &len);
> if (unlikely(!buf)) {
> - pr_debug("%s: rx error: %d buffers missing\n",
> - head_skb->dev->name, hdr->mhdr.num_buffers);
> - head_skb->dev->stats.rx_length_errors++;
> - return -EINVAL;
> + pr_debug("%s: rx error: %d buffers out of %d missing\n",
> + dev->name, num_buf, hdr->mhdr.num_buffers);
> + dev->stats.rx_length_errors++;
> + goto err_buf;
> }
> if (unlikely(len > MAX_PACKET_LEN)) {
> pr_debug("%s: rx error: merge buffer too long\n",
> - head_skb->dev->name);
> + dev->name);
> len = MAX_PACKET_LEN;
> }
> +
> + 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)) {
> struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
> - if (unlikely(!nskb)) {
> - head_skb->dev->stats.rx_dropped++;
> - return -ENOMEM;
> - }
> +
> + if (unlikely(!nskb))
> + goto err_skb;
> if (curr_skb == head_skb)
> skb_shinfo(curr_skb)->frag_list = nskb;
> else
> curr_skb->next = nskb;
> - curr_skb = nskb;
> head_skb->truesize += nskb->truesize;
> + curr_skb = nskb;
> num_skb_frags = 0;
> }
> if (curr_skb != head_skb) {
> @@ -338,8 +350,7 @@ static int receive_mergeable(struct receive_queue *rq,
> struct sk_buff *head_skb)
> head_skb->len += len;
> head_skb->truesize += MAX_PACKET_LEN;
> }
> - page = virt_to_head_page(buf);
> - offset = buf - (char *)page_address(page);
> + offset = buf - page_address(page);
> if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
> put_page(page);
> skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
> @@ -349,9 +360,28 @@ static int receive_mergeable(struct receive_queue *rq,
> struct sk_buff *head_skb)
> offset, len,
> MAX_PACKET_LEN);
> }
> + }
> +
> + return head_skb;
> +
> +err_skb:
> + put_page(page);
> +err_buf:
> + dev->stats.rx_dropped++;
> + dev_kfree_skb(head_skb);
> + while (--num_buf) {
> + buf = virtqueue_get_buf(rq->vq, &len);
> + if (unlikely(!buf)) {
> + pr_debug("%s: rx error: %d buffers missing\n",
> + dev->name, num_buf);
> + dev->stats.rx_length_errors++;
> + break;
> + }
> + page = virt_to_head_page(buf);
> + put_page(page);
> --rq->num;
> }
> - return 0;
> + return NULL;
> }
>
> static void receive_buf(struct receive_queue *rq, void *buf, unsigned int
> len)
> @@ -380,19 +410,9 @@ static void receive_buf(struct receive_queue *rq, void
> *buf, unsigned int len)
> len -= sizeof(struct virtio_net_hdr);
> skb_trim(skb, len);
> } else if (vi->mergeable_rx_bufs) {
> - struct page *page = virt_to_head_page(buf);
> - skb = page_to_skb(rq, page,
> - (char *)buf - (char *)page_address(page),
> - len, MAX_PACKET_LEN);
> - if (unlikely(!skb)) {
> - dev->stats.rx_dropped++;
> - put_page(page);
> + skb = receive_mergeable(dev, rq, buf, len);
> + if (unlikely(!skb))
> return;
> - }
> - if (receive_mergeable(rq, skb)) {
> - dev_kfree_skb(skb);
> - return;
> - }
> } else {
> page = buf;
> skb = page_to_skb(rq, page, 0, len, PAGE_SIZE);
> --
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