linux-kernel - [PATCH] tcp: avoid bogus warning in tcp_clean_rtx

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Date:   Mon, 18 Sep 2017 22:48:47 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] tcp: avoid bogus warning in tcp_clean_rtx_queue

gcc-4.9 warns that it cannot trace the state of the 'last_ackt'
variable since the change to the TCP timestamping code, when
CONFIG_PROFILE_ANNOTATED_BRANCHES is set:

net/ipv4/tcp_input.c: In function 'tcp_clean_rtx_queue':
include/net/tcp.h:757:23: error: 'last_ackt' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Other gcc versions, both older and newer do now show this
warning. Removing the 'likely' annotation makes it go away,
and has no effect on the object code without
CONFIG_PROFILE_ANNOTATED_BRANCHES, as tested with gcc-4.9
and gcc-7.1.1, so this seems to be a safe workaround.

Fixes: 9a568de4818d ("tcp: switch TCP TS option (RFC 7323) to 1ms clock")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c5d7656beeee..c52bc8e35d4d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3173,7 +3173,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
 		flag |= FLAG_SACK_RENEGING;
 
-	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
+	if (first_ackt && !(flag & FLAG_RETRANS_DATA_ACKED)) {
 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
 	}
-- 
2.9.0