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From: Anna-Maria Behnsen <anna-maria@linutronix.de>
To: Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>, 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 V2 25/50] signal: Confine POSIX_TIMERS properly
In-Reply-To: <20240410165552.509700441@linutronix.de>
Date: Wed, 17 Apr 2024 14:09:05 +0200
Message-ID: <875xwg5gym.fsf@somnus>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain

Thomas Gleixner <tglx@linutronix.de> writes:

> Move the itimer rearming out of the signal code and consolidate all posix
> timer related functions in the signal code under one ifdef.

It would be easier to read, when it is splitted. But I made it :)

With the typo fix below feel free to add:

Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>


> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  include/linux/posix-timers.h |    5 +
>  kernel/signal.c              |  125 +++++++++++++++----------------------------
>  kernel/time/itimer.c         |   22 +++++++
>  kernel/time/posix-timers.c   |   15 ++++-
>  4 files changed, 82 insertions(+), 85 deletions(-)
>
> --- a/include/linux/posix-timers.h
> +++ b/include/linux/posix-timers.h

[...]

> @@ -151,7 +151,27 @@ COMPAT_SYSCALL_DEFINE2(getitimer, int, w
>  #endif
>  
>  /*
> - * The timer is automagically restarted, when interval != 0
> + * Invoked from dequeue_signal() when SIG_ALRM is delivered.

s/SIG_ALRM/SIGALRM


> + *
> + * Restart the ITIMER_REAL timer if it is armed as periodic timer.  Doing
> + * this in the signal delivery path instead of self rearming prevents a DoS
> + * with small increments in the high reolution timer case and reduces timer
> + * noise in general.
> + */
> +void posixtimer_rearm_itimer(struct task_struct *tsk)
> +{
> +	struct hrtimer *tmr = &tsk->signal->real_timer;
> +
> +	if (!hrtimer_is_queued(tmr) && tsk->signal->it_real_incr != 0) {
> +		hrtimer_forward(tmr, tmr->base->get_time(),
> +				tsk->signal->it_real_incr);
> +		hrtimer_restart(tmr);
> +	}
> +}
> +
> +/*
> + * Interval timers are restarted in the signal delivery path.  See
> + * posixtimer_rearm_itimer().
>   */
>  enum hrtimer_restart it_real_fn(struct hrtimer *timer)
>  {