[PATCH] timers/itimer: Preserve nonzero remaining time for active timers

[PATCH] timers/itimer: Preserve nonzero remaining time for active timers

[Avi Weiss]

itimer_get_remtime() preserves positive remainders below one
microsecond, but struct timeval only stores whole microseconds.
So, for example, the conversion to tv_usec truncates a 500 ns
remainder to zero, causing getitimer(ITIMER_REAL) to report an
active timer as disarmed.

Clamp active remainders below one microsecond to one microsecond
so they remain nonzero after conversion.

Fixes: 2ff678b8da64 ("[PATCH] hrtimer: switch itimers to hrtimer")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
 kernel/time/itimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index 03a32dffc56c..a472a4f8babb 100644
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -36,7 +36,7 @@ static struct timespec64 itimer_get_remtime(struct hrtimer *timer)
 	 * then we return 0 - which is correct.
 	 */
 	if (hrtimer_active(timer)) {
-		if (rem <= 0)
+		if (rem < NSEC_PER_USEC)
 			rem = NSEC_PER_USEC;
 	} else
 		rem = 0;

base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
-- 
2.43.0

Re: [PATCH] timers/itimer: Preserve nonzero remaining time for active timers

[Frederic Weisbecker]

Le Mon, Nov 02, 2026 at 09:01:49AM +0200, Avi Weiss a écrit :
> itimer_get_remtime() preserves positive remainders below one
> microsecond, but struct timeval only stores whole microseconds.
> So, for example, the conversion to tv_usec truncates a 500 ns
> remainder to zero, causing getitimer(ITIMER_REAL) to report an
> active timer as disarmed.
> 
> Clamp active remainders below one microsecond to one microsecond
> so they remain nonzero after conversion.
> 
> Fixes: 2ff678b8da64 ("[PATCH] hrtimer: switch itimers to hrtimer")
> Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
> ---
>  kernel/time/itimer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
> index 03a32dffc56c..a472a4f8babb 100644
> --- a/kernel/time/itimer.c
> +++ b/kernel/time/itimer.c
> @@ -36,7 +36,7 @@ static struct timespec64 itimer_get_remtime(struct hrtimer *timer)
>  	 * then we return 0 - which is correct.
>  	 */
>  	if (hrtimer_active(timer)) {
> -		if (rem <= 0)
> +		if (rem < NSEC_PER_USEC)
>  			rem = NSEC_PER_USEC;

Right, though at this point it can race with the hrtimer at any point.
But it makes sense to have.

Thanks.

>  	} else
>  		rem = 0;
> 
> base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
> -- 
> 2.43.0
> 

-- 
Frederic Weisbecker
SUSE Labs