[net-next,1/3] tcp: convert icsk_user_timeout from jiffies to msecs

Message ID 20180712003625.2551-1-jmaxwell37@gmail.com
State Changes Requested
Delegated to: David Miller
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  • [net-next,1/3] tcp: convert icsk_user_timeout from jiffies to msecs
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Commit Message

Jon Maxwell July 12, 2018, 12:36 a.m.
This is a preparatory commit for an upcoming patch that improves the socket
TCP_USER_TIMEOUT option accuracy. Implement Eric Dumazets idea to convert 
icsk->icsk_user_timeout from jiffies to msecs. To eliminate the 
msecs_to_jiffies() and jiffies_to_msecs() dance in future. 

There will 3 patches in this series. [net-next, 2/3] will create a seperate 
helper routine called tcp_retransmit_stamp() as per Neal Cardwells suggestion. 
Finally [net-next, 3/3] will implement a new routine called 
tcp_clamp_rto_to_user_timeout() to calculate the rto so that TCP_USER_TIMEOUT
is more accurate. As a result of the final patch it won't have the 
msecs_to_jiffies() and jiffies_to_msecs() dance that David Laight was concerned
about.

Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
---
 net/ipv4/tcp.c       | 4 ++--
 net/ipv4/tcp_timer.c | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

Comments

Eric Dumazet July 12, 2018, 12:35 p.m. | #1
On Thu, Jul 12, 2018 at 1:57 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Jon Maxwell Sent: 12 July 2018 01:36
> ...
> > - (s32)(tcp_time_stamp(tp) - start_ts) >
> > - jiffies_to_msecs(icsk->icsk_user_timeout))
> > + (s32)(tcp_time_stamp(tp) - start_ts) > icsk->icsk_user_timeout)
>
> That has never been tested properly.
> icsk_user_timeout is u32 so the comparison is unsigned and the (s32) cast
> has no effect.
>

The existing code had this ' bug' already.

Please do not blame this patch, and send a patch if you believe there
is an issue ?

In my opinion, the (s32) here is a reminder for the reader of the
width of the expression,
more than anything, since there is no chance the result can be negative.

Patch

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e3704a49164b..9d900162f16a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2984,7 +2984,7 @@  static int do_tcp_setsockopt(struct sock *sk, int level,
 		if (val < 0)
 			err = -EINVAL;
 		else
-			icsk->icsk_user_timeout = msecs_to_jiffies(val);
+			icsk->icsk_user_timeout = val;
 		break;
 
 	case TCP_FASTOPEN:
@@ -3440,7 +3440,7 @@  static int do_tcp_getsockopt(struct sock *sk, int level,
 		break;
 
 	case TCP_USER_TIMEOUT:
-		val = jiffies_to_msecs(icsk->icsk_user_timeout);
+		val = icsk->icsk_user_timeout;
 		break;
 
 	case TCP_FASTOPEN:
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 3b3611729928..fa34984d0b12 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -183,8 +183,9 @@  static bool retransmits_timed_out(struct sock *sk,
 		else
 			timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 				(boundary - linear_backoff_thresh) * TCP_RTO_MAX;
+		timeout = jiffies_to_msecs(timeout);
 	}
-	return (tcp_time_stamp(tcp_sk(sk)) - start_ts) >= jiffies_to_msecs(timeout);
+	return (tcp_time_stamp(tcp_sk(sk)) - start_ts) >= timeout;
 }
 
 /* A write timeout has occurred. Process the after effects. */
@@ -337,8 +338,7 @@  static void tcp_probe_timer(struct sock *sk)
 	if (!start_ts)
 		skb->skb_mstamp = tp->tcp_mstamp;
 	else if (icsk->icsk_user_timeout &&
-		 (s32)(tcp_time_stamp(tp) - start_ts) >
-		 jiffies_to_msecs(icsk->icsk_user_timeout))
+		 (s32)(tcp_time_stamp(tp) - start_ts) > icsk->icsk_user_timeout)
 		goto abort;
 
 	max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
@@ -672,7 +672,7 @@  static void tcp_keepalive_timer (struct timer_list *t)
 		 * to determine when to timeout instead.
 		 */
 		if ((icsk->icsk_user_timeout != 0 &&
-		    elapsed >= icsk->icsk_user_timeout &&
+		    elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&
 		    icsk->icsk_probes_out > 0) ||
 		    (icsk->icsk_user_timeout == 0 &&
 		    icsk->icsk_probes_out >= keepalive_probes(tp))) {