linux-kernel - Re: [PATCH V3 1/3] arm64/mm/hotplug: Register boot memory hot remove notifier earlier

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Message-ID: <bde102b0-7054-ae1d-d5d2-6348f4049d13@redhat.com>
Date:   Wed, 23 Sep 2020 16:04:56 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Mark Rutland <mark.rutland@....com>, Will Deacon <will@...nel.com>,
        catalin.marinas@....com, Steve Capper <steve.capper@....com>,
        linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Marc Zyngier <maz@...nel.org>, will@...nel.org
Subject: Re: [PATCH V3 1/3] arm64/mm/hotplug: Register boot memory hot remove
 notifier earlier

Hi Anshuman,

On 9/21/20 10:05 PM, Anshuman Khandual wrote:
> This moves memory notifier registration earlier in the boot process from
> device_initcall() to early_initcall() which will help in guarding against
> potential early boot memory offline requests. Even though there should not
> be any actual offlinig requests till memory block devices are initialized
> with memory_dev_init() but then generic init sequence might just change in
> future. Hence an early registration for the memory event notifier would be
> helpful. While here, just skip the registration if CONFIG_MEMORY_HOTREMOVE
> is not enabled and also call out when memory notifier registration fails.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Steve Capper <steve.capper@....com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   arch/arm64/mm/mmu.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 

With the following nit-picky comments resolved:

Reviewed-by: Gavin Shan <gshan@...hat.com>

> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62fea1b6..df3b7415b128 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1499,7 +1499,17 @@ static struct notifier_block prevent_bootmem_remove_nb = {
>   
>   static int __init prevent_bootmem_remove_init(void)
>   {
> -	return register_memory_notifier(&prevent_bootmem_remove_nb);
> +	int ret = 0;
> +
> +	if (!IS_ENABLED(CONFIG_MEMORY_HOTREMOVE))
> +		return ret;
> +
> +	ret = register_memory_notifier(&prevent_bootmem_remove_nb);
> +	if (!ret)
> +		return ret;
> +
> +	pr_err("Notifier registration failed - boot memory can be removed\n");
> +	return ret;
>   }

It might be cleaner if the duplicated return statements can be
avoided. Besides, it's always nice to print the errno even though
zero is always returned from register_memory_notifier(). So I guess
you probably need something like below:

         ret = register_memory_notifier(&prevent_bootmem_remove_nb);
         if (ret)
             pr_err("%s: Error %d registering notifier\n", __func__, ret)

         return ret;


register_memory_notifier                   # 0 is returned on !CONFIG_MEMORY_HOTPLUG_SPARSE
    blocking_notifier_chain_register
       notifier_chain_register              # 0 is always returned
       
> -device_initcall(prevent_bootmem_remove_init);
> +early_initcall(prevent_bootmem_remove_init);
>   #endif
> 

Cheers,
Gavin