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Date: Wed, 20 Nov 2013 16:20:32 +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: Re: [PATCH RFC] virtio_net: fix error handling for mergeable buffers
On Wed, Nov 20, 2013 at 08:54:02AM -0500, Jason Wang wrote:
>
>
> ----- 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.
It makes the interfaces too messy. We are not in code freeze in -net -
only feature freeze, so no reason to make code like spagetty,
and it's only 25 lines changed as compared to 40.
It's not a huge refactoring.
It's just as easy to backport my patch too.
You just drop the goto in the new code path we added.
Let me show you (untested) - your patch is not smaller.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
commit 9b442fe970d5c71311d4314edef26ee2eb16e7fb
Author: Michael S. Tsirkin <mst@...hat.com>
Date: Wed Nov 20 12:44:14 2013 +0200
virtio_net: fix resource leak on alloc failure
virtio net got confused, started dropping packets.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9fbdfcd..df4b9d0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -297,13 +297,22 @@ static struct sk_buff *page_to_skb(struct receive_queue *rq,
return skb;
}
-static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
+static struct sk_buff *receive_mergeable(struct net_device *dev,
+ struct receive_queue *rq,
+ struct page *page,
+ unsigned int len)
{
- struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
- struct page *page;
- int num_buf, i, len;
+ struct skb_vnet_hdr *hdr = page_address(buf);
+ int num_buf = hdr->mhdr.num_buffers;
+ struct sk_buff *skb = page_to_skb(rq, page, len);
+ int i;
+
+ skb = page_to_skb(rq, page, len);
+
+ if (unlikely(!skb))
+ goto err_skb;
+
- num_buf = hdr->mhdr.num_buffers;
while (--num_buf) {
i = skb_shinfo(skb)->nr_frags;
if (i >= MAX_SKB_FRAGS) {
@@ -313,10 +322,10 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
}
page = virtqueue_get_buf(rq->vq, &len);
if (!page) {
- pr_debug("%s: rx error: %d buffers missing\n",
- skb->dev->name, hdr->mhdr.num_buffers);
- skb->dev->stats.rx_length_errors++;
- return -EINVAL;
+ pr_debug("%s: rx error: %d buffers %d missing\n",
+ dev->name, hdr->mhdr.num_buffers, num_buf);
+ dev->stats.rx_length_errors++;
+ goto err_buf;
}
if (len > PAGE_SIZE)
@@ -326,7 +335,25 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
--rq->num;
}
- return 0;
+ return 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 = buf;
+ give_pages(rq, page);
+ --rq->num;
+ }
+ return NULL;
}
static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
@@ -354,17 +381,18 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
skb_trim(skb, len);
} else {
page = buf;
- skb = page_to_skb(rq, page, len);
- if (unlikely(!skb)) {
- dev->stats.rx_dropped++;
- give_pages(rq, page);
- return;
- }
- if (vi->mergeable_rx_bufs)
- if (receive_mergeable(rq, skb)) {
- dev_kfree_skb(skb);
+ if (vi->mergeable_rx_bufs) {
+ skb = receive_mergeable(dev, rq, page, len);
+ if (unlikely(!skb))
+ return;
+ } else {
+ skb = page_to_skb(rq, page, len);
+ if (unlikely(!skb)) {
+ dev->stats.rx_dropped++;
+ give_pages(rq, page);
return;
}
+ }
}
hdr = skb_vnet_hdr(skb);
--
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