[PATCH] xen-netback: fix occasional leak of grant ref mappings under memory pressure

[Igor Druzhinin <igor.druzhinin@citrix.com>]

Zero-copy callback flag is not yet set on frag list skb at the moment
xenvif_handle_frag_list() returns -ENOMEM. This eventually results in
leaking grant ref mappings since xenvif_zerocopy_callback() is never
called for these fragments. Those eventually build up and cause Xen
to kill Dom0 as the slots get reused for new mappings.

That behavior is observed under certain workloads where sudden spikes
of page cache usage for writes coexist with active atomic skb allocations.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
---
 drivers/net/xen-netback/netback.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 80aae3a..2023317 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1146,9 +1146,12 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 
 		if (unlikely(skb_has_frag_list(skb))) {
 			if (xenvif_handle_frag_list(queue, skb)) {
+				struct sk_buff *nskb =
+						skb_shinfo(skb)->frag_list;
 				if (net_ratelimit())
 					netdev_err(queue->vif->dev,
 						   "Not enough memory to consolidate frag_list!\n");
+				xenvif_skb_zerocopy_prepare(queue, nskb);
 				xenvif_skb_zerocopy_prepare(queue, skb);
 				kfree_skb(skb);
 				continue;
-- 
2.7.4