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.
>
> - If @from has a fraglist, it is not relevant as we copy it into @to and
> will free @from.
This is going to be a FAQ
http://www.spinics.net/lists/netdev/msg315090.html
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