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Commit b68e9f85 authored by Herbert Xu's avatar Herbert Xu Committed by Linus Torvalds
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[PATCH] tcp: fix TSO cwnd caching bug 



tcp_write_xmit caches the cwnd value indirectly in cwnd_quota.  When
tcp_transmit_skb reduces the cwnd because of tcp_enter_cwr, the cached
value becomes invalid.

This patch ensures that the cwnd value is always reread after each
tcp_transmit_skb call.

Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 846998ae

net/ipv4/tcp_output.c

+9 −25
Original line number Diff line number Diff line
@@ -972,18 +972,17 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) 
	if (unlikely(sk->sk_state == TCP_CLOSE))

		return 0;



	skb = sk->sk_send_head;

	if (unlikely(!skb))

		return 0;



	sent_pkts = 0;

	while ((skb = sk->sk_send_head)) {

		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);

		BUG_ON(!tso_segs);



		cwnd_quota = tcp_cwnd_test(tp, skb);

	if (unlikely(!cwnd_quota))

		goto out;

		if (!cwnd_quota)

			break;



	sent_pkts = 0;

	while (likely(tcp_snd_wnd_test(tp, skb, mss_now))) {

		BUG_ON(!tso_segs);

		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))

			break;



		if (tso_segs == 1) {

			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
@@ -1026,27 +1025,12 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) 


		tcp_minshall_update(tp, mss_now, skb);

		sent_pkts++;



		/* Do not optimize this to use tso_segs. If we chopped up

		 * the packet above, tso_segs will no longer be valid.

		 */

		cwnd_quota -= tcp_skb_pcount(skb);



		BUG_ON(cwnd_quota < 0);

		if (!cwnd_quota)

			break;



		skb = sk->sk_send_head;

		if (!skb)

			break;

		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);

	}



	if (likely(sent_pkts)) {

		tcp_cwnd_validate(sk, tp);

		return 0;

	}

out:

	return !tp->packets_out && sk->sk_send_head;

}