From: Lance Yang <lance.yang@linux.dev>

As Zi pointed out, we should avoid crashing the kernel for conditions
that can be handled gracefully. Encountering a non-anonymous folio in an
anonymous VMA is a bug, but a warning is sufficient.

This patch changes the VM_BUG_ON_FOLIO(!folio_test_anon(folio)) to a
VM_WARN_ON_FOLIO() in both __collapse_huge_page_isolate() and
hpage_collapse_scan_pmd(), and then aborts the scan with SCAN_PAGE_ANON.

Making more of the scanning logic common between hpage_collapse_scan_pmd()
and __collapse_huge_page_isolate(), as suggested by Dev.

Suggested-by: Dev Jain <dev.jain@arm.com>
Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
---
 mm/khugepaged.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 808523f92c7b..87a8df90b3a6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -573,7 +573,11 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		}
 
 		folio = page_folio(page);
-		VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
+		if (!folio_test_anon(folio)) {
+			VM_WARN_ON_FOLIO(true, folio);
+			result = SCAN_PAGE_ANON;
+			goto out;
+		}
 
 		/* See hpage_collapse_scan_pmd(). */
 		if (folio_maybe_mapped_shared(folio)) {
@@ -1335,6 +1339,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		folio = page_folio(page);
 
 		if (!folio_test_anon(folio)) {
+			VM_WARN_ON_FOLIO(true, folio);
 			result = SCAN_PAGE_ANON;
 			goto out_unmap;
 		}
-- 
2.49.0

On 06/10/25 8:13 pm, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> As Zi pointed out, we should avoid crashing the kernel for conditions
> that can be handled gracefully. Encountering a non-anonymous folio in an
> anonymous VMA is a bug, but a warning is sufficient.
>
> This patch changes the VM_BUG_ON_FOLIO(!folio_test_anon(folio)) to a
> VM_WARN_ON_FOLIO() in both __collapse_huge_page_isolate() and
> hpage_collapse_scan_pmd(), and then aborts the scan with SCAN_PAGE_ANON.
>
> Making more of the scanning logic common between hpage_collapse_scan_pmd()
> and __collapse_huge_page_isolate(), as suggested by Dev.
>
> Suggested-by: Dev Jain <dev.jain@arm.com>
> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> ---
>   

Reviewed-by: Dev Jain <dev.jain@arm.com>

On Mon, Oct 06, 2025 at 10:43:37PM +0800, Lance Yang wrote:
>From: Lance Yang <lance.yang@linux.dev>
>
>As Zi pointed out, we should avoid crashing the kernel for conditions
>that can be handled gracefully. Encountering a non-anonymous folio in an
>anonymous VMA is a bug, but a warning is sufficient.
>
>This patch changes the VM_BUG_ON_FOLIO(!folio_test_anon(folio)) to a
>VM_WARN_ON_FOLIO() in both __collapse_huge_page_isolate() and
>hpage_collapse_scan_pmd(), and then aborts the scan with SCAN_PAGE_ANON.
>
>Making more of the scanning logic common between hpage_collapse_scan_pmd()
>and __collapse_huge_page_isolate(), as suggested by Dev.
>
>Suggested-by: Dev Jain <dev.jain@arm.com>
>Suggested-by: Zi Yan <ziy@nvidia.com>
>Signed-off-by: Lance Yang <lance.yang@linux.dev>

Reviewed-by: Wei Yang <richard.weiyang@gmail.com>

-- 
Wei Yang
Help you, Help me