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Message-ID: <20131120132657.GA8455@redhat.com>
Date: Wed, 20 Nov 2013 15:26:57 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...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: [PATCH RFC] virtio_net: fix error handling for mergeable buffers
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.
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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