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

["David Hildenbrand (Arm)" <david@kernel.org>]

On 5/12/26 14:48, Lance Yang wrote:
> 
> 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 ...

Right, likely that should be removed+cleaned up then.

-- 
Cheers,

David