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

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Message-Id: <20180731165041.GX24813@linux.vnet.ibm.com>
Date:   Tue, 31 Jul 2018 09:50:41 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        tglx@...utronix.de, frederic@...nel.org, bristot@...hat.com,
        peterz@...radead.org
Subject: Re: [PATCH] nohz: Fix local_timer_softirq_pending()

On Tue, Jul 31, 2018 at 06:13:58PM +0200, 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.
> 
> Fixes: 5d62c183f9e9 ("nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()")
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

2729 opportunities to change "1UL << x" to "BIT(x)", including
__raise_softirq_irqoff().  I did the two in RCU.  ;-)

							Thanx, Paul

> ---
>  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)
> -- 
> 2.18.0
>