Commit 4e2fd555 authored May 25, 2009 by Lennert Buytenhek Committed by David S. Miller May 25, 2009

gianfar: fix BUG under load after introduction of skb recycling



Since commit 0fd56bb5 ("gianfar:
Add support for skb recycling"), gianfar puts skbuffs that are in
the rx ring back onto the recycle list as-is in case there was a
receive error, but this breaks the following invariant: that all
skbuffs on the recycle list have skb->data = skb->head + NET_SKB_PAD.

The RXBUF_ALIGNMENT realignment done in gfar_new_skb() will be done
twice on skbuffs recycled in this way, causing there not to be enough
room in the skb anymore to receive a full packet, eventually leading
to an skb_over_panic from gfar_clean_rx_ring() -> skb_put().

Resetting the skb->data pointer to skb->head + NET_SKB_PAD before
putting the skb back onto the recycle list restores the mentioned
invariant, and should fix this issue.

Reported-by: Michael Guntsche <mike@it-loops.com>
Tested-by: Michael Guntsche <mike@it-loops.com>
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 0975ecba

drivers/net/gianfar.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -1885,8 +1885,17 @@ int gfar_clean_rx_ring(struct net_device *dev, int rx_work_limit)

		if (unlikely(!newskb))
		newskb = skb;
		else if (skb)
		else if (skb) {
		/*
		* We need to reset ->data to what it
		* was before gfar_new_skb() re-aligned
		* it to an RXBUF_ALIGNMENT boundary
		* before we put the skb back on the
		* recycle list.
		*/
		skb->data = skb->head + NET_SKB_PAD;
		__skb_queue_head(&priv->rx_recycle, skb);
		}
		} else {
		/* Increment the number of packets */
		dev->stats.rx_packets++;

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