Re: [PATCH v8 3/6] mm/memory-failure: report MF_MSG_KERNEL for unrecoverable kernel pages

[David Hildenbrand (Arm)]

On 5/27/26 16:06, Breno Leitao wrote:
> The previous patch teaches get_any_page() to return -ENOTRECOVERABLE
> for stable unhandlable kernel pages (PG_reserved, slab, page tables,
> large-kmalloc).  memory_failure() still folds every negative return
> into MF_MSG_GET_HWPOISON, so callers that want to react to the
> unrecoverable cases (a panic option, smarter logging) cannot tell
> them apart from transient page-allocator races.
> 
> Turn the post-call branch into a switch over the get_hwpoison_page()
> return code: map -ENOTRECOVERABLE to MF_MSG_KERNEL and any other
> negative return to MF_MSG_GET_HWPOISON.  case 0 keeps the existing
> free-buddy / kernel-high-order handling and case 1 falls through to
> the rest of memory_failure() unchanged.
> 
> The MF_MSG_KERNEL label and tracepoint string are kept as
> "reserved kernel page" to avoid breaking userspace tools that match
> on those literals; the enum value still adequately tags the failure
> even though it now also covers slab, page tables and large-kmalloc
> pages.
> 
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
>  mm/memory-failure.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 8f63bdfeff8f..14c0a958638c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2426,7 +2426,8 @@ int memory_failure(unsigned long pfn, int flags)
>  	 * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
>  	 */
>  	res = get_hwpoison_page(p, flags);
> -	if (!res) {
> +	switch (res) {
> +	case 0:
>  		if (is_free_buddy_page(p)) {
>  			if (take_page_off_buddy(p)) {
>  				page_ref_inc(p);
> @@ -2445,7 +2446,19 @@ int memory_failure(unsigned long pfn, int flags)
>  			res = action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
>  		}
>  		goto unlock_mutex;
> -	} else if (res < 0) {
> +	case 1:
> +		/* Got a refcount on a handlable page. */
> +		break;
> +	case -ENOTRECOVERABLE:
> +		/*
> +		 * Stable unhandlable kernel-owned page (PG_reserved,
> +		 * slab, page tables, large-kmalloc).
> +		 * No recovery possible.
> +		 */
> +		res = action_result(pfn, MF_MSG_KERNEL, MF_IGNORED);
> +		goto unlock_mutex;
> +	default:
> +		/* Transient lifecycle race with the page allocator. */
>  		res = action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
>  		goto unlock_mutex;
>  	}
> 

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David