linux-kernel - Re: [PATCH] nohz: Fix local_timer_softirq

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Date:   Tue, 31 Jul 2018 19:07:45 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Anna-Maria Gleixner <anna-maria@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     bigeasy@...utronix.de, tglx@...utronix.de, frederic@...nel.org,
        paulmck@...ux.vnet.ibm.com, peterz@...radead.org
Subject: Re: [PATCH] nohz: Fix local_timer_softirq_pending()

On 07/31/2018 06:13 PM, Anna-Maria Gleixner wrote:
> local_timer_softirq_pending() checks whether the timer softirq is
> pending with: local_softirq_pending() & TIMER_SOFTIRQ.
> 
> This is wrong because TIMER_SOFTIRQ is the softirq number and not a
> bitmask. So the test checks for the wrong bit.
> 
> Use BIT(TIMER_SOFTIRQ) instead.

Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>

Thanks!
-- Daniel

> Fixes: 5d62c183f9e9 ("nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()")
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> ---
>  kernel/time/tick-sched.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index da9455a6b42b..5b33e2f5c0ed 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -642,7 +642,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
>  
>  static inline bool local_timer_softirq_pending(void)
>  {
> -	return local_softirq_pending() & TIMER_SOFTIRQ;
> +	return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
>  }
>  
>  static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
>