[ 073/167] [PATCH 13/26] net: allow pskb_expand_head() to get maximum tailroom

From: Ben Hutchings
Date: Wed May 09 2012 - 02:19:56 EST

3.2-stable review patch. If anyone has any objections, please let me know.


From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

[ Upstream commit 87151b8689d890dfb495081f7be9b9e257f7a2df ]

Marc Merlin reported many order-1 allocations failures in TX path on its
wireless setup, that dont make any sense with MTU=1500 network, and non
SG capable hardware.

Turns out part of the problem comes from pskb_expand_head() not using
ksize() to get exact head size given by kmalloc(). Doing the same thing
than __alloc_skb() allows more tailroom in skb and can prevent future

As a bonus, struct skb_shared_info becomes cache line aligned.

Reported-by: Marc MERLIN <marc@xxxxxxxxxxx>
Tested-by: Marc MERLIN <marc@xxxxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
net/core/skbuff.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 29cb392..2ec200de 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -903,9 +903,11 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
goto adjust_others;

- data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
+ data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
+ gfp_mask);
if (!data)
goto nodata;
+ size = SKB_WITH_OVERHEAD(ksize(data));

/* Copy only real data... and, alas, header. This should be
* optimized for the cases when header is void.

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