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

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Date:   Thu, 24 Sep 2020 08:53:47 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.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



On 09/23/2020 11:34 AM, Gavin Shan wrote:
> 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

Thought about it, just that the error message was too long.

> 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;

Sure, will do.

> 
> 
> 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
> 
>