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>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index baf8d281152c..e59840010d45 100644
--- 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.