linux-kernel - Re: [patch V3 17/18] posix-timers: Provide a mechanism to allocate a given timer ID

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Message-ID: <Z9CsstMf-EVZpsiH@pavilion.home>
Date: Tue, 11 Mar 2025 22:35:46 +0100
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>,
	Benjamin Segall <bsegall@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: [patch V3 17/18] posix-timers: Provide a mechanism to allocate a
 given timer ID

Le Sat, Mar 08, 2025 at 05:48:47PM +0100, Thomas Gleixner a écrit :
> @@ -364,6 +389,16 @@ static enum hrtimer_restart posix_timer_
>  	return HRTIMER_NORESTART;
>  }
>  
> +long posixtimer_create_prctl(unsigned long ctrl)
> +{
> +	if (ctrl > PR_TIMER_CREATE_RESTORE_IDS_ON)
> +		return -EINVAL;
> +
> +	guard(spinlock_irq)(&current->sighand->siglock);
> +	current->signal->timer_create_restore_ids = ctrl == PR_TIMER_CREATE_RESTORE_IDS_ON;

Is the locking necessary here? It's not used on the read side.
It only makes sense if more flags are to be added later in struct signal and the
fields write can race.

Also do we want to carry this PR_TIMER_CREATE_RESTORE_IDS_ON accross exec? Posix
timers are removed then anyway.

Thanks.