Re: WARNING: at net/ipv4/tcp.c:1610 tcp_recvmsg+0xb1b/0xc70()

Eric Dumazet
2012-05-27T19:36:20Z

On Sun, 2012-05-27 at 20:13 +0100, Jack Stone wrote:
> On 05/27/2012 06:35 PM, Eric Dumazet wrote:
> > So it seems we can queue in sk_receive_queue a packet with SYN flag set.
> >
> > (A SYN or SYNACK packet contains DATA payload...)
> >
> > The sequence number of such frames should be tweaked (seq++) instead of
> > games we do in fast path :
> >
> > if (tcp_hdr(skb)->syn)
> > offset--;
> >
> >
> > Oh well this can wait linux-3.6, please test following patch in the
> > meantime.
> >
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index b224eb8..34c8dcc 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -4553,7 +4553,7 @@ static bool tcp_try_coalesce(struct sock *sk,
> >
> > *fragstolen = false;
> >
> > - if (tcp_hdr(from)->fin)
> > + if (tcp_hdr(from)->fin || tcp_hdr(to)->syn)
> > return false;
> >
> > /* Its possible this segment overlaps with prior segment in queue */
> >
> >
>
> Still seems to fire with the above applied, it also sets of the warn just above it...
>
> Could it be something to do with my staging network driver?

Yes it could be memory corruption.

(making tcp _think_ tcp_hdr(skb)->syn is set, while it was not at all.

Please replace debugging patch by following, because tcp flags are
copied elsewhere, so we can double check.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3ba605f..22e4c9a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1606,8 +1606,10 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
if (tcp_hdr(skb)->fin)
goto found_fin_ok;
WARN(!(flags & MSG_PEEK),
- "recvmsg bug 2: copied %X seq %X rcvnxt %X fl %X\n",
- *seq, TCP_SKB_CB(skb)->seq, tp->rcv_nxt, flags);
+ "recvmsg bug 2: copied %X seq %X end_seq %X rcvnxt %X fl %X offset %u len %u syn %d tcp_flags %X\n",
+ *seq, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
+ tp->rcv_nxt, flags, offset, skb->len, tcp_hdr(skb)->syn,
+ TCP_SKB_CB(skb)->tcp_flags);
}

/* Well, if we have backlog, try to process it now yet. */