[PATCH] mm/page_alloc: Fix freeing of failed-split poisoned compound pages

[PATCH] mm/page_alloc: Fix freeing of failed-split poisoned compound pages

[Boudewijn van der Heide]

free_pages_prepare() only handles poisoned order-0 pages.
In memory_failure() (hard offline), pages
are poisoned before attempting to split huge pages. If the split fails,
the page remains a compound (order > 0) but is already poisoned. However,
Soft-offline pages are always poisoned as order-0 after migration, so
they are unaffected.

The '!order' check causes these poisoned compound pages to skip
poison handling, leaving them in the buddy allocator.

Worst case, a poisoned compound page could be reallocated,
potentially leading to crashes, silent data corruption,
or unwanted memory containment actions before the poison bit is detected.

This patch removes the '&& !order' restriction. Cleanup functions in the
poison-handling block correctly handle non-zero order pages, making
this change safe.

Fixes: 79f5f8fab482 ("mm,hwpoison: rework soft offline for in-use pages")
Signed-off-by: Boudewijn van der Heide <boudewijn@delta-utec.com>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c380f063e8b7..64d15e56706c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1344,7 +1344,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
 	}
 
-	if (unlikely(PageHWPoison(page)) && !order) {
+	if (unlikely(PageHWPoison(page))) {
 		/* Do not let hwpoison pages hit pcplists/buddy */
 		reset_page_owner(page, order);
 		page_table_check_free(page, order);
-- 
2.47.3

Re: [PATCH] mm/page_alloc: Fix freeing of failed-split poisoned compound pages

[Zi Yan]

Add Miaohe (memory failure maintainer)

On 13 Jan 2026, at 15:54, Boudewijn van der Heide wrote:

> free_pages_prepare() only handles poisoned order-0 pages.
> In memory_failure() (hard offline), pages
> are poisoned before attempting to split huge pages. If the split fails,
> the page remains a compound (order > 0) but is already poisoned. However,
> Soft-offline pages are always poisoned as order-0 after migration, so
> they are unaffected.
>
> The '!order' check causes these poisoned compound pages to skip
> poison handling, leaving them in the buddy allocator.
>
> Worst case, a poisoned compound page could be reallocated,
> potentially leading to crashes, silent data corruption,
> or unwanted memory containment actions before the poison bit is detected.
>
> This patch removes the '&& !order' restriction. Cleanup functions in the
> poison-handling block correctly handle non-zero order pages, making
> this change safe.

This is not a fix. IIUC, for >0 order free pages, memory failure uses
take_page_off_buddy() in a different code path.

Miaohe (cc’d) should be able to elaborate more on it.

>
> Fixes: 79f5f8fab482 ("mm,hwpoison: rework soft offline for in-use pages")
> Signed-off-by: Boudewijn van der Heide <boudewijn@delta-utec.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c380f063e8b7..64d15e56706c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1344,7 +1344,7 @@ __always_inline bool free_pages_prepare(struct page *page,
>  		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
>  	}
>
> -	if (unlikely(PageHWPoison(page)) && !order) {
> +	if (unlikely(PageHWPoison(page))) {
>  		/* Do not let hwpoison pages hit pcplists/buddy */
>  		reset_page_owner(page, order);
>  		page_table_check_free(page, order);
> -- 
> 2.47.3


Best Regards,
Yan, Zi

Re: [PATCH] mm/page_alloc: Fix freeing of failed-split poisoned compound pages

[Boudewijn van der Heide]

> > free_pages_prepare() only handles poisoned order-0 pages.
> > In memory_failure() (hard offline), pages
> > are poisoned before attempting to split huge pages. If the split fails,
> > the page remains a compound (order > 0) but is already poisoned. However,
> > Soft-offline pages are always poisoned as order-0 after migration, so
> > they are unaffected.
> >
> > The '!order' check causes these poisoned compound pages to skip
> > poison handling, leaving them in the buddy allocator.
> >
> > Worst case, a poisoned compound page could be reallocated,
> > potentially leading to crashes, silent data corruption,
> > or unwanted memory containment actions before the poison bit is detected.
> >
> > This patch removes the '&& !order' restriction. Cleanup functions in the
> > poison-handling block correctly handle non-zero order pages, making
> > this change safe.

> This is not a fix. IIUC, for >0 order free pages, memory failure uses
> take_page_off_buddy() in a different code path.
>

Thanks again for the quick response and clarification! 
From my understanding, 
you correctly noted that take_page_off_buddy() handles already-free pages, 
removing them from the buddy lists and setting SetPageHWPoisonTakenOff(). 
This prevents those pages from re-entering the buddy allocator.

My concern is about in-use THP-backed compound pages:
1. A compound page is in use. 
2. memory_failure() marks it poisoned (TestSetPageHWPoison).
3. try_to_split_thp_page() fails.
4. The process using the THP may be killed; 
        the page remains compound and poisoned.
5. Later, when the page is finally freed, it reaches free_pages_prepare();
        'take_page_off_buddy()' is not invoked in this path.

At this point, the current check:

'if (unlikely(PageHWPoison(page)) && !order)'

will not trigger, because the order > 0.

> Miaohe (cc’d) should be able to elaborate more on it.
Thanks for Cc'ing Miaohe, hopefully Miaohe can provide some more insights!

Thanks,
Boudewijn