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Message-ID: <CANn89iKFH_F0_Ri76Zsez2Nn8JZ9obprsk+OE7i+enGC=n8Syw@mail.gmail.com>
Date: Fri, 27 Jul 2018 20:13:19 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] tcp: propagate GSO to the new skb built in
tcp collapse
On Fri, Jul 27, 2018 at 8:02 PM Yafang Shao <laoar.shao@...il.com> wrote:
>
> Currently the collapsed SKB doesn't propagate the GSO information to the
> new SKB.
> The GSO should be propagated for better tracking, i.e. when this SKB is
> dropped we could know how many network segments are dropped.
What is "the GSO" ?
>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
> net/ipv4/tcp_input.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 90f83eb..af52e4e 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -4893,6 +4893,8 @@ void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
> if (!nskb)
> break;
>
> + skb_shinfo(nskb)->gso_size = skb_shinfo(skb)->gso_size;
> + skb_shinfo(nskb)->gso_type = skb_shinfo(skb)->gso_type;
Why gso_size and gso_type are important ?
Where later in the stack these values are used ?
> memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
> #ifdef CONFIG_TLS_DEVICE
> nskb->decrypted = skb->decrypted;
> @@ -4906,18 +4908,24 @@ void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
>
> /* Copy data, releasing collapsed skbs. */
> while (copy > 0) {
> - int offset = start - TCP_SKB_CB(skb)->seq;
> int size = TCP_SKB_CB(skb)->end_seq - start;
> + int offset = start - TCP_SKB_CB(skb)->seq;
>
> BUG_ON(offset < 0);
> if (size > 0) {
> - size = min(copy, size);
> + if (copy >= size)
> + skb_shinfo(nskb)->gso_segs +=
> + max_t(u16, 1, skb_shinfo(skb)->gso_segs);
> + else
> + size = copy;
> +
So... what happens if copy was partial ?
Your patch does not really fix the uncertainty, it merely shifts it a bit.
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