+ mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/khugepaged: use VM_WARN_ON_FOLIO instead of VM_BUG_ON_FOLIO for non-anon folios
has been added to the -mm mm-new branch.  Its filename is
     mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Lance Yang <lance.yang@linux.dev>
Subject: mm/khugepaged: use VM_WARN_ON_FOLIO instead of VM_BUG_ON_FOLIO for non-anon folios
Date: Wed, 8 Oct 2025 12:37:47 +0800

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.

Link: https://lkml.kernel.org/r/20251008043748.45554-3-lance.yang@linux.dev
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Suggested-by: Dev Jain <dev.jain@arm.com>
Suggested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/mm/khugepaged.c~mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios
+++ a/mm/khugepaged.c
@@ -573,7 +573,11 @@ static int __collapse_huge_page_isolate(
 		}
 
 		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)) {
@@ -1340,6 +1344,7 @@ static int hpage_collapse_scan_pmd(struc
 		folio = page_folio(page);
 
 		if (!folio_test_anon(folio)) {
+			VM_WARN_ON_FOLIO(true, folio);
 			result = SCAN_PAGE_ANON;
 			goto out_unmap;
 		}
_

Patches currently in -mm which might be from lance.yang@linux.dev are

hung_task-fix-warnings-caused-by-unaligned-lock-pointers.patch
mm-khugepaged-abort-collapse-scan-on-non-swap-entries.patch
mm-khugepaged-optimize-pte-scanning-with-if-else-if-else-if-chain.patch
mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios.patch
mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper.patch