linux-kernel - Re: [PATCH 4/6] posix-cpu-timers: Force next

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Date:   Wed, 16 Jun 2021 11:23:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 4/6] posix-cpu-timers: Force next_expiration recalc after
 timer reset

On Fri, Jun 04, 2021 at 01:31:57PM +0200, Frederic Weisbecker wrote:

> @@ -647,8 +651,6 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
>  	if (unlikely(timer->it.cpu.firing)) {
>  		timer->it.cpu.firing = -1;
>  		ret = TIMER_RETRY;
> -	} else {
> -		cpu_timer_dequeue(ctmr);
>  	}
>  
>  	/*
> @@ -713,9 +715,13 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
>  	 * For a timer with no notification action, we don't actually
>  	 * arm the timer (we'll just fake it for timer_gettime).
>  	 */
> -	cpu_timer_setexpires(ctmr, new_expires);
> -	if (new_expires != 0 && val < new_expires) {
> -		arm_timer(timer, p);
> +	if (new_expires != 0) {
> +		cpu_timer_dequeue(ctmr);
> +		cpu_timer_setexpires(ctmr, new_expires);
> +		if (val < new_expires)
> +			arm_timer(timer, p);
> +	} else {
> +		disarm_timer(timer, p);
>  	}
>  
>  	unlock_task_sighand(p, &flags);

AFAICT there's an error path in between where you've removed
cpu_timer_dequeue() and added it back. This error path will now leave
the timer enqueued.