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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: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Duyck 2012-05-02 18:18:42 +00:00 committed by David S. Miller
parent b081f85c29
commit 2996d31f9f
2 changed files with 7 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
net/core/skbuff.c
View File

@ -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;

9
net/ipv4/tcp_input.c
View File

@ -4589,7 +4589,7 @@ copyfrags:
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 @@ copyfrags:
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;
*fragstolen = true;
delta = len; /* we dont know real truesize... */
goto copyfrags;
}