linux-kernel - Re: [patch 17/45] posix-cpu-timers: Make k_itimer::it

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Date:   Tue, 4 Jul 2023 00:30:46 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        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 17/45] posix-cpu-timers: Make k_itimer::it_active
 consistent

On Tue, Jun 06, 2023 at 04:37:45PM +0200, Thomas Gleixner wrote:
> @@ -787,6 +790,7 @@ static u64 collect_timerqueue(struct tim
>  
>  	while ((next = timerqueue_getnext(head))) {
>  		struct cpu_timer *ctmr;
> +		struct k_itimer *ktmr;
>  		u64 expires;
>  
>  		ctmr = container_of(next, struct cpu_timer, node);
> @@ -799,6 +803,8 @@ static u64 collect_timerqueue(struct tim
>  		/* See posix_cpu_timer_wait_running() */
>  		rcu_assign_pointer(ctmr->handling, current);
>  		cpu_timer_dequeue(ctmr);
> +		ktmr = container_of(ctmr, struct k_itimer, it.cpu);
> +		ktmr->it_active = 0;

Maybe move this to cpu_timer_fire() because:

1) Other posix-timer implementation set it_active = 0
   from their actual handler.

2) This place doesn't have the timer locked. Better Make
   sure we have this protection to avoid mistakes against
   potential future use of it_active.

Thanks.

>  		list_add_tail(&ctmr->elist, firing);
>  	}
>  
>