linux-kernel - Re: [PATCH 2/2] random: spread out jitter callback to different CPUs

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Message-ID: <Yz55w4gNtZn8JzmG@linutronix.de>
Date:   Thu, 6 Oct 2022 08:46:27 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Sultan Alsawaf <sultan@...neltoast.com>
Subject: Re: [PATCH 2/2] random: spread out jitter callback to different CPUs

On 2022-10-05 23:08:19 [+0200], Jason A. Donenfeld wrote:
> Hi Sebastian,
Hi Jason,

> On Wed, Oct 05, 2022 at 07:26:42PM +0200, Sebastian Andrzej Siewior wrote:
> > That del_timer_sync() at the end is what you want. If the timer is
> > pending (as in enqueued in the timer wheel) then it will be removed
> > before it is invoked. If the timer's callback is invoked then it will
> > spin until the callback is done.
> 
> del_timer_sync() is not guaranteed to succeed with add_timer_on() being
> used in conjunction with timer_pending() though. That's why I've
> abandoned this.

But why? The timer is added to a timer-base on a different CPU. Should
work.

> Jason

Sebastian