Commit fb93134d authored Nov 14, 2007 by Herbert Xu Committed by David S. Miller Nov 14, 2007

[TCP]: Fix size calculation in sk_stream_alloc_pskb



We round up the header size in sk_stream_alloc_pskb so that
TSO packets get zero tail room.  Unfortunately this rounding
up is not coordinated with the select_size() function used by
TCP to calculate the second parameter of sk_stream_alloc_pskb.

As a result, we may allocate more than a page of data in the
non-TSO case when exactly one page is desired.

In fact, rounding up the head room is detrimental in the non-TSO
case because it makes memory that would otherwise be available to
the payload head room.  TSO doesn't need this either, all it wants
is the guarantee that there is no tail room.

So this patch fixes this by adjusting the skb_reserve call so that
exactly the requested amount (which all callers have calculated in
a precise way) is made available as tail room.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 18b2b7bd

include/net/sock.h

+6 −4

Original line number	Diff line number	Diff line
		@@ -1235,14 +1235,16 @@ static inline struct sk_buff sk_stream_alloc_pskb(struct sock sk,
		gfp_t gfp)
		{
		struct sk_buff *skb;
		int hdr_len;

		hdr_len = SKB_DATA_ALIGN(sk->sk_prot->max_header);
		skb = alloc_skb_fclone(size + hdr_len, gfp);
		skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp);
		if (skb) {
		skb->truesize += mem;
		if (sk_stream_wmem_schedule(sk, skb->truesize)) {
		skb_reserve(skb, hdr_len);
		/*
		* Make sure that we have exactly size bytes
		* available to the caller, no more, no less.
		*/
		skb_reserve(skb, skb_tailroom(skb) - size);
		return skb;
		}
		__kfree_skb(skb);

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