linux-kernel - Re: [patch V2 31/50] posix-timers: Add proper state tracking

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Date: Wed, 17 Apr 2024 15:40:36 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>, John Stultz
 <jstultz@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar
 <mingo@...nel.org>, Stephen Boyd <sboyd@...nel.org>, Eric Biederman
 <ebiederm@...ssion.com>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [patch V2 31/50] posix-timers: Add proper state tracking

Thomas Gleixner <tglx@...utronix.de> writes:

> Right now the state tracking is done by two struct members:
>
>  - it_active:
>      A boolean which tracks armed/disarmed state
>
>  - it_signal_seq:
>      A sequence counter which is used to invalidate settings
>      and prevent rearming
>
> Replace it_active with it_status and keep properly track about the states
> in one place.
>
> This allows to reuse it_signal_seq to track reprogramming, disarm and
> delete operations in order to drop signals which are related to the state
> previous of those operations.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

[...]

> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -453,7 +453,6 @@ static void disarm_timer(struct k_itimer
>  	struct cpu_timer *ctmr = &timer->it.cpu;
>  	struct posix_cputimer_base *base;
>  
> -	timer->it_active = 0;
>  	if (!cpu_timer_dequeue(ctmr))
>  		return;
>  
> @@ -494,11 +493,12 @@ static int posix_cpu_timer_del(struct k_
>  		 */
>  		WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
>  	} else {
> -		if (timer->it.cpu.firing)
> +		if (timer->it.cpu.firing) {
>  			ret = TIMER_RETRY;
> -		else
> +		} else {
>  			disarm_timer(timer, p);
> -
> +			timer->it_status = POSIX_TIMER_DISARMED;
> +		}
>  		unlock_task_sighand(p, &flags);
>  	}

Why do you move the update of the it_status here and do not reuse the
place where you added the it_active in patch 21 "posix-cpu-timers: Make
k_itimer::it_active consistent"? Then the update of the state would
still be next to cpu_timer_dequeue().

[...]

> @@ -647,10 +650,10 @@ void common_timer_get(struct k_itimer *t
>  	/* interval timer ? */
>  	if (iv) {
>  		cur_setting->it_interval = ktime_to_timespec64(iv);
> -	} else if (!timr->it_active) {
> +	} else if (timr->it_status == POSIX_TIMER_DISARMED) {
>  		/*
>  		 * SIGEV_NONE oneshot timers are never queued and therefore
> -		 * timr->it_active is always false. The check below
> +		 * timr->it_status is always DISARMED. The check below

s/DISARMED/POSIX_TIMER_DISARMED/

This change would help when using grep.

>  		 * vs. remaining time will handle this case.
>  		 *
>  		 * For all other timers there is nothing to update here, so