From c137f3dda04b0aee1bc6889cdc69185f53df8a82 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ilpo=20J=C3=A4rvinen?= Date: Mon, 7 Apr 2008 22:32:38 -0700 Subject: [PATCH] [TCP]: Fix NewReno's fast rexmit/recovery problems with GSOed skb MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Fixes a long-standing bug which makes NewReno recovery crippled. With GSO the whole head skb was marked as LOST which is in violation of NewReno procedure that only wants to mark one packet and ended up breaking our TCP code by causing counter overflow because our code was built on top of assumption about valid NewReno procedure. This manifested as triggering a WARN_ON for the overflow in a number of places. It seems relatively safe alternative to just do nothing if tcp_fragment fails due to oom because another duplicate ACK is likely to be received soon and the fragmentation will be retried. Special thanks goes to Soeren Sonnenburg who was lucky enough to be able to reproduce this so that the warning for the overflow was hit. It's not as easy task as it seems even if this bug happens quite often because the amount of outstanding data is pretty significant for the mismarkings to lead to an overflow. Because it's very late in 2.6.25-rc cycle (if this even makes in time), I didn't want to touch anything with SACK enabled here. Fragmenting might be useful for it as well but it's more or less a policy decision rather than mandatory fix. Thus there's no need to rush and we can postpone considering tcp_fragment with SACK for 2.6.26. In 2.6.24 and earlier, this very same bug existed but the effect is slightly different because of a small changes in the if conditions that fit to the patch's context. With them nothing got lost marker and thus no retransmissions happened. Signed-off-by: Ilpo Järvinen Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 5573202f086..7d0958785bf 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2138,7 +2138,9 @@ static void tcp_mark_head_lost(struct sock *sk, int packets) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; - int cnt; + int cnt, oldcnt; + int err; + unsigned int mss; BUG_TRAP(packets <= tp->packets_out); if (tp->lost_skb_hint) { @@ -2157,13 +2159,25 @@ static void tcp_mark_head_lost(struct sock *sk, int packets) tp->lost_skb_hint = skb; tp->lost_cnt_hint = cnt; + if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq)) + break; + + oldcnt = cnt; if (tcp_is_fack(tp) || tcp_is_reno(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) cnt += tcp_skb_pcount(skb); - if ((cnt > packets) || - after(TCP_SKB_CB(skb)->end_seq, tp->high_seq)) - break; + if (cnt > packets) { + if (tcp_is_sack(tp) || (oldcnt >= packets)) + break; + + mss = skb_shinfo(skb)->gso_size; + err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss); + if (err < 0) + break; + cnt = packets; + } + if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) { TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out += tcp_skb_pcount(skb); -- 2.41.1