linux-kernel - Re: [PATCH 1/2] kernel/cpu: add arch override for clear_tasks_mm

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Date:   Fri, 20 Nov 2020 11:06:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anton Vorontsov <anton.vorontsov@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kernel/cpu: add arch override for
 clear_tasks_mm_cpumask() mm handling

On Fri, Nov 20, 2020 at 12:57:56PM +1000, Nicholas Piggin wrote:
> powerpc keeps a counter in the mm which counts bits set in mm_cpumask as
> well as other things. This means it can't use generic code to clear bits
> out of the mask and doesn't adjust the arch specific counter.
> 
> Add an arch override allowing powerpc to use clear_tasks_mm_cpumask().
> 
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>

Seems reasonable enough..

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
>  kernel/cpu.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6ff2578ecf17..2b8d7a5db383 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -815,6 +815,10 @@ void __init cpuhp_threads_init(void)
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> +#ifndef arch_clear_mm_cpumask_cpu
> +#define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
> +#endif
> +
>  /**
>   * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
>   * @cpu: a CPU id
> @@ -850,7 +854,7 @@ void clear_tasks_mm_cpumask(int cpu)
>  		t = find_lock_task_mm(p);
>  		if (!t)
>  			continue;
> -		cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
> +		arch_clear_mm_cpumask_cpu(cpu, t->mm);
>  		task_unlock(t);
>  	}
>  	rcu_read_unlock();
> -- 
> 2.23.0
>