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SubjectRe: [PATCH V3 1/3] arm64/mm/hotplug: Register boot memory hot remove notifier earlier
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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@arm.com>
> Cc: Will Deacon <will@kernel.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Steve Capper <steve.capper@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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@redhat.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

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