Commit 843925f3 authored Jan 01, 2015 by Herbert Xu Committed by David S. Miller Jan 02, 2015

tcp: Do not apply TSO segment limit to non-TSO packets



Thomas Jarosch reported IPsec TCP stalls when a PMTU event occurs.

In fact the problem was completely unrelated to IPsec.  The bug is
also reproducible if you just disable TSO/GSO.

The problem is that when the MSS goes down, existing queued packet
on the TX queue that have not been transmitted yet all look like
TSO packets and get treated as such.

This then triggers a bug where tcp_mss_split_point tells us to
generate a zero-sized packet on the TX queue.  Once that happens
we're screwed because the zero-sized packet can never be removed
by ACKs.

Fixes: 1485348d ("tcp: Apply device TSO segment limit earlier")
Reported-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Cheers,
Signed-off-by: David S. Miller <davem@davemloft.net>

parent c484994e

net/ipv4/tcp_output.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -2019,7 +2019,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
	if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
	break;		break;

	if (tso_segs == 1) {		if (tso_segs == 1 \|\| !max_segs) {
	if (unlikely(!tcp_nagle_test(tp, skb, mss_now,		if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
	(tcp_skb_is_last(sk, skb) ?		(tcp_skb_is_last(sk, skb) ?
	nonagle : TCP_NAGLE_PUSH))))		nonagle : TCP_NAGLE_PUSH))))
	@@ -2032,7 +2032,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
	}		}

	limit = mss_now;		limit = mss_now;
	if (tso_segs > 1 && !tcp_urg_mode(tp))		if (tso_segs > 1 && max_segs && !tcp_urg_mode(tp))
	limit = tcp_mss_split_point(sk, skb, mss_now,		limit = tcp_mss_split_point(sk, skb, mss_now,
	min_t(unsigned int,		min_t(unsigned int,
	cwnd_quota,		cwnd_quota,

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