在 2015/8/28 12:37, Eric Dumazet 写道:
On Fri, 2015-08-28 at 11:35 +0800, Weilong Chen wrote:
Thanks for reply.
On Wed, 2015-08-26 at 19:12 -0700, Eric Dumazet wrote:
On Thu, 2015-08-27 at 08:56 +0800, chenweil...@huawei.com wrote:
From: Weilong Chen <chenweil...@huawei.com>
When try to merge several skbs to prior one, if the frag_list is
used and the the last one is a small packet, once the condition
"len <= skb_tailroom(to)" is satisfied, we will get a wrong
packet!
This patch just check frag_lists before the condtion to prevent
this from happening.
Signed-off-by: Weilong Chen <chenweil...@huawei.com>
---
net/core/skbuff.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8a725cc..d08edcb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4133,6 +4133,9 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff
*from,
if (skb_cloned(to))
return false;
+ if (skb_has_frag_list(to) || skb_has_frag_list(from))
+ return false;
+
if (len <= skb_tailroom(to)) {
if (len)
BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
@@ -4140,9 +4143,6 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff
*from,
return true;
}
- if (skb_has_frag_list(to) || skb_has_frag_list(from))
- return false;
-
if (skb_headlen(from) != 0) {
struct page *page;
unsigned int offset;
Sigh.
No idea what problem you tried to solve.
This patch is not needed.
If (len <= skb_tailroom()), then it is obviously correct to copy_bits()
the bytes.
Hints :
- If @to has a fraglist, then skb_tailroom(to) is 0 so the copy can not
be done.
How to make sure it?
In my test, @to has a fraglist, but skb_tailroom(to) is not 0!
The test is about tipc, the function tipc_buf_append will merge 3 skbs
to one:
packet 1: len = 1420 skb_tailroom = 190
packet 2: len = 1420
packet 2 will be add to 1' fraglist, but not update skb_tailroom
packet 3: len = 60
Here's the error!
Then fix tipc, or make sure you read and understood the code.
By definition, if one skb has something in fraglist, it is non linear.
If you read skb_tailroom(), you'll see this function returns 0 if skb is
non linear.
Yes you'er right, when packet 2 is add to 1' fraglist, tipc should
update the packet 1' 'len' and 'data_len'. In my kernel(v3.10), it
doesn't do that, which was corrected in commit 5074a (v3.16).
Thanks for your patience
include/linux/skbuff.h-/**
include/linux/skbuff.h: * skb_tailroom - bytes at buffer end
include/linux/skbuff.h- * @skb: buffer to check
include/linux/skbuff.h- *
include/linux/skbuff.h- * Return the number of bytes of free space at the
tail of an sk_buff
include/linux/skbuff.h- */
include/linux/skbuff.h:static inline int skb_tailroom(const struct sk_buff *skb)
include/linux/skbuff.h-{
include/linux/skbuff.h- return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
include/linux/skbuff.h-}
.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
