linux-kernel - [PATCH mm-new v2 2/3] mm/khugepaged: use VM_WARN_ON_FOLIO instead of VM_BUG_ON

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Message-ID: <20251006144338.96519-3-lance.yang@linux.dev>
Date: Mon,  6 Oct 2025 22:43:37 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: akpm@...ux-foundation.org,
	david@...hat.com,
	lorenzo.stoakes@...cle.com
Cc: ziy@...dia.com,
	baolin.wang@...ux.alibaba.com,
	Liam.Howlett@...cle.com,
	npache@...hat.com,
	ryan.roberts@....com,
	dev.jain@....com,
	baohua@...nel.org,
	ioworker0@...il.com,
	richard.weiyang@...il.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH mm-new v2 2/3] mm/khugepaged: use VM_WARN_ON_FOLIO instead of VM_BUG_ON_FOLIO for non-anon folios

From: Lance Yang <lance.yang@...ux.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@....com>
Suggested-by: Zi Yan <ziy@...dia.com>
Signed-off-by: Lance Yang <lance.yang@...ux.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