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From:   Artem Savkov <asavkov@redhat.com>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Anna-Maria Behnsen <anna-maria@linutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Artem Savkov <asavkov@redhat.com>
Subject: [PATCH v5 2/2] net: make tcp keepalive timer upper bound
Date:   Thu,  5 May 2022 15:18:11 +0200
Message-Id: <20220505131811.3744503-3-asavkov@redhat.com>
In-Reply-To: <20220505131811.3744503-1-asavkov@redhat.com>
References: <87zgkwjtq2.ffs@tglx>
 <20220505131811.3744503-1-asavkov@redhat.com>
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Make sure TCP keepalive timer does not expire late. Switching to upper
bound timers means it can fire off early but in case of keepalive
tcp_keepalive_timer() handler checks elapsed time and resets the timer
if it was triggered early. This results in timer "cascading" to a
higher precision and being just a couple of milliseconds off it's
original mark.
This adds minimal overhead as keepalive timers are never re-armed and
are usually quite long.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
---
 net/ipv4/inet_connection_sock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 1e5b53c2bb26..bb2dbfb6f5b5 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -589,7 +589,7 @@ EXPORT_SYMBOL(inet_csk_delete_keepalive_timer);
 
 void inet_csk_reset_keepalive_timer(struct sock *sk, unsigned long len)
 {
-	sk_reset_timer(sk, &sk->sk_timer, jiffies + len);
+	sk_reset_timer(sk, &sk->sk_timer, jiffies + upper_bound_timeout(len));
 }
 EXPORT_SYMBOL(inet_csk_reset_keepalive_timer);
 
-- 
2.34.1