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Date:   Mon, 3 Jul 2023 23:12:28 +0200
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Anna-Maria Behnsen <anna-maria@linutronix.de>,
        John Stultz <jstultz@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: [patch 16/45] posix-timers: Consolidate timer setup
Message-ID: <ZKM5vMK_F32Qwg98@localhost.localdomain>
References: <20230606132949.068951363@linutronix.de>
 <20230606142031.928021762@linutronix.de>
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Le Tue, Jun 06, 2023 at 04:37:44PM +0200, Thomas Gleixner a ?crit :
> hrtimer based and CPU timers have their own way to install the new interval
> and to reset overrun and signal handling related data.
> 
> Create a helper function and do the same operation for all variants.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  kernel/time/posix-cpu-timers.c |   15 +--------------
>  kernel/time/posix-timers.c     |   23 +++++++++++++++++------
>  kernel/time/posix-timers.h     |    1 +
>  3 files changed, 19 insertions(+), 20 deletions(-)
> 
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -709,21 +709,8 @@ static int posix_cpu_timer_set(struct k_
>  		trigger_base_recalc_expires(timer, p);
>  
>  	unlock_task_sighand(p, &flags);
> -	/*
> -	 * Install the new reload setting, and
> -	 * set up the signal and overrun bookkeeping.
> -	 */
> -	timer->it_interval = timespec64_to_ktime(new->it_interval);
>  
> -	/*
> -	 * This acts as a modification timestamp for the timer,
> -	 * so any automatic reload attempt will punt on seeing
> -	 * that we have reset the timer manually.
> -	 */
> -	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
> -		~REQUEUE_PENDING;
> -	timer->it_overrun_last = 0;
> -	timer->it_overrun = -1;
> +	posix_timer_set_common(timer, new);

So before this patch if a posix cpu timer is set with:

   .it_value = 0,
   .it_interval = 5

a further retrieval would return the same. But after this patch
it will return:

   .it_value = 0,
   .it_interval = 0

That's an ABI change, not sure if it matters though...