Re: [PATCH v6 4/4] mm/hwpoison: introduce per-memory_block hwpoison counter

[Oscar Salvador]

On Fri, Oct 07, 2022 at 10:07:06AM +0900, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> 
> Currently PageHWPoison flag does not behave well when experiencing memory
> hotremove/hotplug.  Any data field in struct page is unreliable when the
> associated memory is offlined, and the current mechanism can't tell whether
> a memory block is onlined because a new memory devices is installed or
> because previous failed offline operations are undone.  Especially if
> there's a hwpoisoned memory, it's unclear what the best option is.
> 
> So introduce a new mechanism to make struct memory_block remember that
> a memory block has hwpoisoned memory inside it. And make any online event
> fail if the onlining memory block contains hwpoison.  struct memory_block
> is freed and reallocated over ACPI-based hotremove/hotplug, but not over
> sysfs-based hotremove/hotplug.  So the new counter can distinguish these
> cases.
> 
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>

I glanzed over it and looks good overall.
Have a small question though:

> @@ -864,6 +878,7 @@ void remove_memory_block_devices(unsigned long start, unsigned long size)
>  		mem = find_memory_block_by_id(block_id);
>  		if (WARN_ON_ONCE(!mem))
>  			continue;
> +		num_poisoned_pages_sub(-1UL, memblk_nr_poison(mem));

Why does num_poisoned_pages_sub() have to make this distinction (!-1 == -1)
for the hot-remove stage?


-- 
Oscar Salvador
SUSE Labs