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gianfar: fix BUG under load after introduction of skb recycling 

Since commit 0fd56bb5be ("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>
This commit is contained in:
Lennert Buytenhek 2009-05-25 00:42:34 -07:00 committed by David S. Miller
parent 0975ecba3b
commit 4e2fd55519
1 changed files with 10 additions and 1 deletions
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11
drivers/net/gianfar.c
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@ -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++;