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Commit 1fd63041 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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net: pskb_expand_head() optimization 



pskb_expand_head() blindly takes references on fragments before calling
skb_release_data(), potentially releasing these references.

We can add a fast path, avoiding these atomic operations, if we own the
last reference on skb->head.

Based on a previous patch from David

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9d348af4

net/core/skbuff.c

+20 −5
Original line number Diff line number Diff line
@@ -779,6 +779,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 
	u8 *data;

	int size = nhead + (skb_end_pointer(skb) - skb->head) + ntail;

	long off;

	bool fastpath;



	BUG_ON(nhead < 0);
@@ -800,6 +801,20 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 
	       skb_shinfo(skb),

	       offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));



	/* Check if we can avoid taking references on fragments if we own

	 * the last reference on skb->head. (see skb_release_data())

	 */

	if (!skb->cloned)

		fastpath = true;

	else {

		int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;



		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;

	}



	if (fastpath) {

		kfree(skb->head);

	} else {

		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)

			get_page(skb_shinfo(skb)->frags[i].page);
@@ -807,7 +822,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 
			skb_clone_fraglist(skb);



		skb_release_data(skb);



	}

	off = (data + nhead) - skb->head;



	skb->head     = data;