On Fri, Jun 5, 2015 at 9:16 AM, Martin KaFai Lau <ka...@fb.com> wrote:
> The problem is caught by this WARN_ON(len > skb->len) in tcp_fragment():
>
> [<ffffffff810510ca>] warn_slowpath_null+0x1a/0x20
> [<ffffffff8160ec90>] tcp_fragment+0x2a0/0x2b0
> [<ffffffff81604e06>] tcp_mark_head_lost+0x196/0x230
> [<ffffffff8160585d>] tcp_update_scoreboard+0x4d/0x80
> [<ffffffff8160a9ac>] tcp_fastretrans_alert+0x6ac/0xa90
> [<ffffffff8160b834>] tcp_ack+0x9d4/0x10e0
> [<ffffffff8160c699>] tcp_rcv_established+0x309/0x7e0
>
> The WARN_ON pointed out that tcp_skb_pcount (i.e.
> TCP_SKB_CB(skb)->tcp_gso_segs) and skb->len is inconsistent.
>
> The WARN_ON stack goes away after setting net.ipv4.tcp_mtu_probing to 0.
>
> This patch is to set the pcount after skb_pull() was called
> in tcp_mtu_probe().
>
> Signed-off-by: Martin KaFai Lau <ka...@fb.com>
> Reported-by: Grant Zhang <gzh...@fastly.com>
> Cc: Eric Dumazet <eduma...@google.com>
> Cc: Neal Cardwell <ncardw...@google.com>
> Cc: Yuchung Cheng <ych...@google.com>
> ---
> net/ipv4/tcp_output.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index a369e8a..6c95c28 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1984,8 +1984,9 @@ static int tcp_mtu_probe(struct sock *sk)
> skb->len, 0);
> } else {
> __pskb_trim_head(skb, copy);
> - tcp_set_skb_tso_segs(sk, skb, mss_now);
> }
> + tcp_set_skb_tso_segs(sk, skb, mss_now);
> +
> TCP_SKB_CB(skb)->seq += copy;
> }
>
>
Sounds good, although I would simply get rid of all this complexity in
this very unlikely path.
Would you instead try the following ?
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index
eeb59befaf06867b00e1dd6ded7742b2f0bcd821..41ef2c96b2e810e289d6d773e4be09c493b99c09
100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1987,16 +1987,7 @@ static int tcp_mtu_probe(struct sock *sk)
} else {
TCP_SKB_CB(nskb)->tcp_flags |=
TCP_SKB_CB(skb)->tcp_flags &
~(TCPHDR_FIN|TCPHDR_PSH);
- if (!skb_shinfo(skb)->nr_frags) {
- skb_pull(skb, copy);
- if (skb->ip_summed != CHECKSUM_PARTIAL)
- skb->csum = csum_partial(skb->data,
- skb->len, 0);
- } else {
- __pskb_trim_head(skb, copy);
- tcp_set_skb_tso_segs(sk, skb, mss_now);
- }
- TCP_SKB_CB(skb)->seq += copy;
+ tcp_trim_head(sk, skb, copy);
}
len += copy;
--
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