net: allow pskb_expand_head() to get maximum tailroom

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
reallocations.

As a bonus, struct skb_shared_info becomes cache line aligned.

Reported-by: Marc MERLIN <marc@merlins.org>
Tested-by: Marc MERLIN <marc@merlins.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index baf8d28..e598400 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -952,9 +952,11 @@ 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.