linux-kernel - Re: [RFC PATCH 5/7] lazy tlb: introduce lazy mm refcount helper functions

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Message-ID: <20200710094800.GA4800@hirez.programming.kicks-ass.net>
Date:   Fri, 10 Jul 2020 11:48:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-arch@...r.kernel.org, x86@...nel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        Anton Blanchard <anton@...abs.org>
Subject: Re: [RFC PATCH 5/7] lazy tlb: introduce lazy mm refcount helper
 functions

On Fri, Jul 10, 2020 at 11:56:44AM +1000, Nicholas Piggin wrote:

> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 73199470c265..ad95812d2a3f 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1253,7 +1253,7 @@ void start_secondary(void *unused)
>  	unsigned int cpu = smp_processor_id();
>  	struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
>  
> -	mmgrab(&init_mm);
> +	mmgrab(&init_mm); /* XXX: where is the mmput for this? */
>  	current->active_mm = &init_mm;
>  
>  	smp_store_cpu_info(cpu);

Right; so IIRC it should be this one:

> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 134688d79589..ff9fcbc4e76b 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -578,7 +578,7 @@ static int finish_cpu(unsigned int cpu)
>  	 */
>  	if (mm != &init_mm)
>  		idle->active_mm = &init_mm;
> -	mmdrop(mm);
> +	mmdrop_lazy_tlb(mm);
>  	return 0;
>  }