Commit 9202e31d authored May 04, 2012 by Alexander Duyck Committed by David S. Miller May 06, 2012

skb: Drop bad code from pskb_expand_head

The fast-path for pskb_expand_head contains a check where the size plus the
unaligned size of skb_shared_info is compared against the size of the data
buffer. This code path has two issues. First is the fact that after the
recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info
is always placed in the optimal spot for a buffer size making this check
unnecessary. The second issue is the fact that the check doesn't take into
account the aligned size of shared info. As a result the code burns cycles
doing a memcpy with nothing actually being shifted.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent bd14b1b2

net/core/skbuff.c

+0 −12

Original line number	Diff line number	Diff line
		@@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
		}

		if (fastpath && !skb->head_frag &&
		size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
		memmove(skb->head + size, skb_shinfo(skb),
		offsetof(struct skb_shared_info,
		frags[skb_shinfo(skb)->nr_frags]));
		memmove(skb->head + nhead, skb->head,
		skb_tail_pointer(skb) - skb->head);
		off = nhead;
		goto adjust_others;
		}

		data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
		gfp_mask);
		if (!data)
		@@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,

		skb->head = data;
		skb->head_frag = 0;
		adjust_others:
		skb->data += off;
		#ifdef NET_SKBUFF_DATA_USES_OFFSET
		skb->end = size;