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Date:   Mon, 30 Jul 2018 14:36:31 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Pavel Tatashin <pasha.tatashin@oracle.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        LKML <linux-kernel@vger.kernel.org>, mingo@kernel.org,
        tglx@linutronix.de, hpa@zytor.com,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/timers] sched/clock: Enable sched clock early
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On Tue, Jul 24, 2018 at 10:41:19PM -0400, Pavel Tatashin wrote:

> If we need it, we can surround the sched_clock_register() with
> local_irq_disable/local_irq_enable:
> 
> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> index cbc72c2c1fca..5015b165b55b 100644
> --- a/kernel/time/sched_clock.c
> +++ b/kernel/time/sched_clock.c
> @@ -243,8 +243,11 @@ void __init generic_sched_clock_init(void)
>          * If no sched_clock() function has been provided at that point,
>          * make it the final one one.
>          */
> -       if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
> +       if (cd.actual_read_sched_clock == jiffy_sched_clock_read) {
> +               local_irq_disable();
>                 sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
> +               local_irq_enable();
> +       }
> 
>         update_sched_clock();

I'm thinking maybe disable IRQs for that entire function, instead of
just the register call.