linux-kernel - [tip: timers/core] timekeeping: Fix cross-timestamp interpolation on counter wrap

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Date: Mon, 19 Feb 2024 16:35:17 -0000
From: "tip-bot2 for Peter Hilber" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Peter Hilber <peter.hilber@...nsynergy.com>,
 Thomas Gleixner <tglx@...utronix.de>, John Stultz <jstultz@...gle.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timekeeping: Fix cross-timestamp interpolation on
 counter wrap

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     84dccadd3e2a3f1a373826ad71e5ced5e76b0c00
Gitweb:        https://git.kernel.org/tip/84dccadd3e2a3f1a373826ad71e5ced5e76b0c00
Author:        Peter Hilber <peter.hilber@...nsynergy.com>
AuthorDate:    Mon, 18 Dec 2023 08:38:39 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 19 Feb 2024 12:18:51 +01:00

timekeeping: Fix cross-timestamp interpolation on counter wrap

cycle_between() decides whether get_device_system_crosststamp() will
interpolate for older counter readings.

cycle_between() yields wrong results for a counter wrap-around where after
< before < test, and for the case after < test < before.

Fix the comparison logic.

Fixes: 2c756feb18d9 ("time: Add history to cross timestamp interface supporting slower devices")
Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: John Stultz <jstultz@...gle.com>
Link: https://lore.kernel.org/r/20231218073849.35294-2-peter.hilber@opensynergy.com

---
 kernel/time/timekeeping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 266d028..8f35455 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1186,7 +1186,7 @@ static bool cycle_between(u64 before, u64 test, u64 after)
 {
 	if (test > before && test < after)
 		return true;
-	if (test < before && before > after)
+	if (before > after && (test > before || test < after))
 		return true;
 	return false;
 }