Re: [PATCH v4 2/3] mm/memory-failure: add panic option for unrecoverable pages

[Miaohe Lin]

On 2026/4/22 23:21, Breno Leitao wrote:
> Hello Miaohe,
> 
> On Wed, Apr 22, 2026 at 11:36:11AM +0800, Miaohe Lin wrote:
>> On 2026/4/15 20:55, Breno Leitao wrote:
>>> Add a sysctl panic_on_unrecoverable_memory_failure that triggers a
>>> kernel panic when memory_failure() encounters pages that cannot be
>>> recovered. This provides a clean crash with useful debug information
>>> rather than allowing silent data corruption.
>>>
>>> The panic is triggered for three categories of unrecoverable failures,
>>> all requiring result == MF_IGNORED:
>>>
>>> - MF_MSG_KERNEL: reserved pages identified via PageReserved.
>>>
>>> - MF_MSG_KERNEL_HIGH_ORDER: pages with refcount 0 that are not in the
>>>   buddy allocator (e.g., tail pages of high-order kernel allocations).
>>>   A TOCTOU race between get_hwpoison_page() and is_free_buddy_page()
>>>   is possible when CONFIG_DEBUG_VM is disabled, since check_new_pages()
>>>   is gated by is_check_pages_enabled() and becomes a no-op. Panicking
>>>   is still correct: the physical memory has a hardware error regardless
>>>   of who allocated the page.
>>
>> What if the page is used by userspace? We can recover from later accessing.
>> Would panic here be overkill?
> 
> A userspace page should not reach the MF_MSG_KERNEL_HIGH_ORDER branch. The
> branch is gated on get_hwpoison_page() == 0, i.e., folio_try_get() observed
> _refcount == 0, and that condition rules out a live userspace mapping, no?

Sorry, I didn't express myself clearly. What I mean is, a buddy page currently
being allocated could reach the MF_MSG_KERNEL_HIGH_ORDER branch. This page might
be allocated to a userspace. In this case, we can recover from later accessing.
But with your patch, panic will be triggered instead.

> 
> are you suggesting I drop MF_MSG_KERNEL_HIGH_ORDER from here, or, document this
> will not hit userspace pages?

No, maybe we should rule out or document above rare case if I'm not miss something.

Thanks.
.