[RFC PATCH v3 1/7] timekeeping: Fix cross-timestamp interpolation on counter wrap

From: Peter Hilber <peter.hilber@opensynergy.com>
To: linux-kernel@vger.kernel.org
Cc: Peter Hilber <peter.hilber@opensynergy.com>,
	John Stultz <jstultz@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stephen Boyd <sboyd@kernel.org>,
	"Christopher S. Hall" <christopher.s.hall@intel.com>
Subject: [RFC PATCH v3 1/7] timekeeping: Fix cross-timestamp interpolation on counter wrap
Date: Mon, 18 Dec 2023 08:38:39 +0100	[thread overview]
Message-ID: <20231218073849.35294-2-peter.hilber@opensynergy.com> (raw)
In-Reply-To: <20231218073849.35294-1-peter.hilber@opensynergy.com>

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@opensynergy.com>
Acked-by: John Stultz <jstultz@google.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 0ff065c5d25b..08a3d0052baa 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;
 }
-- 
2.40.1

