Re: [PATCH v6 1/4] mm/memory-failure: report MF_MSG_KERNEL for reserved pages

[Lance Yang <lance.yang@linux.dev>]

On Tue, May 12, 2026 at 10:17:00AM +0200, David Hildenbrand (Arm) wrote:
>On 5/11/26 17:38, Breno Leitao wrote:
>> When get_hwpoison_page() returns a negative value, distinguish
>> reserved pages from other failure cases by reporting MF_MSG_KERNEL
>> instead of MF_MSG_GET_HWPOISON. Reserved pages belong to the kernel
>> and should be classified accordingly for proper handling.
>> 
>> Sample PG_reserved before the get_hwpoison_page() call. In the
>> MF_COUNT_INCREASED path get_any_page() can drop the caller's
>> reference before returning -EIO, after which the underlying page may
>> have been freed and reallocated with page->flags reset; reading
>> PageReserved(p) at that point would observe stale or unrelated state.
>> The pre-call snapshot reflects what the page actually was at the
>> time of the failure event.
>> 
>> Acked-by: Miaohe Lin <linmiaohe@huawei.com>
>> Reviewed-by: Lance Yang <lance.yang@linux.dev>
>> Signed-off-by: Breno Leitao <leitao@debian.org>
>> ---
>>  mm/memory-failure.c | 19 ++++++++++++++++++-
>>  1 file changed, 18 insertions(+), 1 deletion(-)
>> 
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 866c4428ac7ef..f112fb27a8ff6 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -2348,6 +2348,7 @@ int memory_failure(unsigned long pfn, int flags)
>>  	unsigned long page_flags;
>>  	bool retry = true;
>>  	int hugetlb = 0;
>> +	bool is_reserved;
>>  
>>  	if (!sysctl_memory_failure_recovery)
>>  		panic("Memory failure on page %lx", pfn);
>> @@ -2411,6 +2412,18 @@ int memory_failure(unsigned long pfn, int flags)
>>  	 * In fact it's dangerous to directly bump up page count from 0,
>>  	 * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
>>  	 */
>> +	/*
>> +	 * Pages with PG_reserved set are not currently managed by the
>> +	 * page allocator (memblock-reserved memory, driver reservations,
>> +	 * etc.), so classify them as kernel-owned for reporting.
>> +	 *
>> +	 * Sample the flag before get_hwpoison_page(): in the
>> +	 * MF_COUNT_INCREASED path, get_any_page() can drop the caller's
>> +	 * reference before returning -EIO, after which page->flags may
>> +	 * have been reset by the allocator.
>> +	 */
>> +	is_reserved = PageReserved(p);
>> +
>>  	res = get_hwpoison_page(p, flags);
>>  	if (!res) {
>>  		if (is_free_buddy_page(p)) {
>> @@ -2432,7 +2445,11 @@ int memory_failure(unsigned long pfn, int flags)
>>  		}
>>  		goto unlock_mutex;
>>  	} else if (res < 0) {
>> -		res = action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
>> +		if (is_reserved)
>> +			res = action_result(pfn, MF_MSG_KERNEL, MF_IGNORED);
>> +		else
>> +			res = action_result(pfn, MF_MSG_GET_HWPOISON,
>> +					    MF_IGNORED);
>>  		goto unlock_mutex;
>>  	}
>>  
>> 
>
>It's a bit odd that we need this handling when we already have handling for
>reserved pages in error_states[].
>
>HWPoisonHandlable() would always essentially reject PG_reserved pages. So
>__get_hwpoison_page() ... would always fail? Making
>get_hwpoison_page()->get_any_page() always fail?
>
>But then, we never call identify_page_state()? And never call me_kernel()?

Looks like we never get that far ...

>This all looks very odd.
>
>Why would you even want to call get_hwpoison_page() in the first place if you
>find PageReserved?

Ah, I see :)

For a PG_reserved page, I would not expect PageLRU to be set, nor would
I expect it to be in the buddy allocator.

include/linux/page-flags.h also says:

"
Once (if ever) freed, PG_reserved is cleared and they will be given to
the page allocator.
"

So maybe special-case PageReserved() before get_hwpoison_page()?
Something like:

	if (PageReserved(p)){
		res = action_result(pfn, MF_MSG_KERNEL, MF_IGNORED);
		goto unlock_mutex; 	
	}

	res = get_hwpoison_page(p, flags, &gp_status);

Cheers, Lance