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Commit 9202e31

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Alexander Duyckdavem330
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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>
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net/core/skbuff.c

Lines changed: 0 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
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fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
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}
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if (fastpath && !skb->head_frag &&
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size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
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memmove(skb->head + size, skb_shinfo(skb),
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offsetof(struct skb_shared_info,
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frags[skb_shinfo(skb)->nr_frags]));
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memmove(skb->head + nhead, skb->head,
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skb_tail_pointer(skb) - skb->head);
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off = nhead;
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goto adjust_others;
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}
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data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
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gfp_mask);
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if (!data)
@@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
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skb->head = data;
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skb->head_frag = 0;
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adjust_others:
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skb->data += off;
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#ifdef NET_SKBUFF_DATA_USES_OFFSET
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skb->end = size;

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