Commit ca44ac38 authored by Changli Gao's avatar Changli Gao Committed by David S. Miller
Browse files

net: don't reallocate skb->head unless the current one hasn't the needed extra size or is shared 



skb head being allocated by kmalloc(), it might be larger than what
actually requested because of discrete kmem caches sizes. Before
reallocating a new skb head, check if the current one has the needed
extra size.

Do this check only if skb head is not shared.

Signed-off-by: default avatarChangli Gao <xiaosuo@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 289700db

net/core/skbuff.c

+23 −11
Original line number Diff line number Diff line
@@ -778,6 +778,28 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 


	size = SKB_DATA_ALIGN(size);



	/* 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 &&

	    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 + sizeof(struct skb_shared_info), gfp_mask);

	if (!data)

		goto nodata;
@@ -791,17 +813,6 @@ 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 {
@@ -816,6 +827,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 
	off = (data + nhead) - skb->head;



	skb->head     = data;

adjust_others:

	skb->data    += off;

#ifdef NET_SKBUFF_DATA_USES_OFFSET

	skb->end      = size;

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