[PATCH net] virtio-net: fix page refcnt leaking when fail to allocate frag skb

[Jason Wang <jasowang@redhat.com>]

We need to drop the refcnt of page when we fail to allocate an skb for frag
list, otherwise it will be leaked. The bug was introduced by commit
2613af0ed18a11d5c566a81f9a6510b73180660a ("virtio_net: migrate mergeable rx
buffers to page frag allocators").

Cc: Michael Dalton <mwdalton@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
The patch was needed for 3.12 stable.
---
 drivers/net/virtio_net.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 69ad42b..3798517 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -322,9 +322,11 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *head_skb)
 				 head_skb->dev->name);
 			len = MERGE_BUFFER_LEN;
 		}
+		page = virt_to_head_page(buf);
 		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
 			struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
 			if (unlikely(!nskb)) {
+				put_page(page);
 				head_skb->dev->stats.rx_dropped++;
 				return -ENOMEM;
 			}
@@ -341,7 +343,6 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *head_skb)
 			head_skb->len += len;
 			head_skb->truesize += MERGE_BUFFER_LEN;
 		}
-		page = virt_to_head_page(buf);
 		offset = buf - (char *)page_address(page);
 		if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
 			put_page(page);
-- 
1.8.3.2