2023-12-18 07:41:41

by Peter Hilber

Subject: [RFC PATCH v3 1/7] 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 <[email protected]>
Acked-by: John Stultz <[email protected]>
---
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

2024-02-19 16:36:13

by tip-bot2 for Jacob Pan

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 <[email protected]>
AuthorDate: Mon, 18 Dec 2023 08:38:39 +01:00
Committer: Thomas Gleixner <[email protected]>
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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: John Stultz <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

---
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;
}