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Commit 2996d31f authored by Alexander Duyck's avatar Alexander Duyck Committed by David S. Miller
Browse files

net: Stop decapitating clones that have a head_frag 



This change is meant ot prevent stealing the skb->head to use as a page in
the event that the skb->head was cloned.  This allows the other clones to
track each other via shinfo->dataref.

Without this we break down to two methods for tracking the reference count,
one being dataref, the other being the page count.  As a result it becomes
difficult to track how many references there are to skb->head.

Signed-off-by: default avatarAlexander Duyck <alexander.h.duyck@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b081f85c

net/core/skbuff.c

+5 −4
Original line number Diff line number Diff line
@@ -1699,17 +1699,18 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe, 
			      struct splice_pipe_desc *spd, struct sock *sk)

{

	int seg;

	bool head_is_linear = !skb->head_frag;

	bool head_is_locked = !skb->head_frag || skb_cloned(skb);



	/* map the linear part :

	 * If skb->head_frag is set, this 'linear' part is backed

	 * by a fragment, and we can avoid a copy.

	 * If skb->head_frag is set, this 'linear' part is backed by a

	 * fragment, and if the head is not shared with any clones then

	 * we can avoid a copy since we own the head portion of this page.

	 */

	if (__splice_segment(virt_to_page(skb->data),

			     (unsigned long) skb->data & (PAGE_SIZE - 1),

			     skb_headlen(skb),

			     offset, len, skb, spd,

			     head_is_linear,

			     head_is_locked,

			     sk, pipe))

		return true;

net/ipv4/tcp_input.c

+2 −7
Original line number Diff line number Diff line
@@ -4589,7 +4589,7 @@ static bool tcp_try_coalesce(struct sock *sk, 
		to->data_len += len;

		goto merge;

	}

	if (from->head_frag) {

	if (from->head_frag && !skb_cloned(from)) {

		struct page *page;

		unsigned int offset;
@@ -4599,12 +4599,7 @@ static bool tcp_try_coalesce(struct sock *sk, 
		offset = from->data - (unsigned char *)page_address(page);

		skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,

				   page, offset, skb_headlen(from));



		if (skb_cloned(from))

			get_page(page);

		else

		*fragstolen = true;



		delta = len; /* we dont know real truesize... */

		goto copyfrags;

	}