linux-kernel - Re: [PATCH] hrtimer: Use raw_cpu_ptr() in clock_was

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Date:   Fri, 13 Aug 2021 08:42:35 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [PATCH] hrtimer: Use raw_cpu_ptr() in clock_was_set()

On 12.08.2021 22:31, Thomas Gleixner wrote:
> clock_was_set() can be invoked from preemptible context. Use raw_cpu_ptr()
> to check whether high resolution mode is active or not. It does not matter
> whether the task migrates after acquiring the pointer.
>
> Fixes: e71a4153b7c2 ("hrtimer: Force clock_was_set() handling for the HIGHRES=n, NOHZ=y case")
> Reported-by: Mike Galbraith <efault@....de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

This fixes the following issue:

BUG: using smp_processor_id() in preemptible [00000000] code: hwclock/227

> ---
>   kernel/time/hrtimer.c |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -944,10 +944,11 @@ static bool update_needs_ipi(struct hrti
>    */
>   void clock_was_set(unsigned int bases)
>   {
> +	struct hrtimer_cpu_base *cpu_base = raw_cpu_ptr(&hrtimer_bases);
>   	cpumask_var_t mask;
>   	int cpu;
>   
> -	if (!hrtimer_hres_active() && !tick_nohz_active)
> +	if (!__hrtimer_hres_active(cpu_base) && !tick_nohz_active)
>   		goto out_timerfd;
>   
>   	if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
> @@ -958,9 +959,9 @@ void clock_was_set(unsigned int bases)
>   	/* Avoid interrupting CPUs if possible */
>   	cpus_read_lock();
>   	for_each_online_cpu(cpu) {
> -		struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
>   		unsigned long flags;
>   
> +		cpu_base = &per_cpu(hrtimer_bases, cpu);
>   		raw_spin_lock_irqsave(&cpu_base->lock, flags);
>   
>   		if (update_needs_ipi(cpu_base, bases))
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland