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mm-khugepaged-fix-folio-is-used-after-folio_put-unlock.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Oct 7 Stable branch

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The quilt patch titled
Subject: mm: khugepaged: fix folio is used after folio_put/unlock()
has been removed from the -mm tree. Its filename was
mm-khugepaged-fix-folio-is-used-after-folio_put-unlock.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Vernon Yang <[email protected]>
Subject: mm: khugepaged: fix folio is used after folio_put/unlock()
Date: Wed, 9 Sep 2026 10:58:03 +0800

On the rollback path, folio_put() has already dropped the last reference of new_folio. On the success path, new_folio is already unlocked and can be freed concurrently. The trace_mm_khugepaged_collapse_file() is left with a dangling folio pointer.

So using the folio_pfn() before dropping the reference, closing use-after-free window.

Link https://lore.kernel.org/[email protected] open here
Fixes 4c9473e87e75 ("mm/khugepaged: add tracepoint to collapse_file()")
Signed-off-by Vernon Yang <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Acked-by David Hildenbrand (Arm) <[email protected]>
Acked-by Lorenzo Stoakes (ARM) <[email protected]>
Cc Barry Song <[email protected]>
Cc Dev Jain <[email protected]>
Cc Lance Yang <[email protected]>
Cc Ryan Roberts <[email protected]>
Cc Zach O'Keefe <[email protected]>
Cc <[email protected]>

---

 include/trace/events/huge_memory.h |    6 +++---
 mm/khugepaged.c                    |    4 +++-
 2 files changed, 6 insertions(+), 4 deletions(-)
include/trace/events/huge_memory.h renamed from include/trace/events/huge_memory.h~mm-khugepaged-fix-folio-is-used-after-folio_put-unlock +3 -3
@@ -211,10 +211,10 @@ TRACE_EVENT(mm_khugepaged_scan_file,
 );
 
 TRACE_EVENT(mm_khugepaged_collapse_file,
-	TP_PROTO(struct mm_struct *mm, struct folio *new_folio, pgoff_t index,
+	TP_PROTO(struct mm_struct *mm, unsigned long new_pfn, pgoff_t index,
 			unsigned long addr, bool is_shmem, struct file *file,
 			int nr, int result),
-	TP_ARGS(mm, new_folio, index, addr, is_shmem, file, nr, result),
+	TP_ARGS(mm, new_pfn, index, addr, is_shmem, file, nr, result),
 	TP_STRUCT__entry(
 		__field(struct mm_struct *, mm)
 		__field(unsigned long, hpfn)

@@ -228,7 +228,7 @@ TRACE_EVENT(mm_khugepaged_collapse_file,
 
 	TP_fast_assign(
 		__entry->mm = mm;
-		__entry->hpfn = new_folio ? folio_pfn(new_folio) : -1;
+		__entry->hpfn = new_pfn;
 		__entry->index = index;
 		__entry->addr = addr;
 		__entry->is_shmem = is_shmem;
mm/khugepaged.c renamed from mm/khugepaged.c~mm-khugepaged-fix-folio-is-used-after-folio_put-unlock +3 -1
@@ -2253,6 +2253,7 @@ static enum scan_result collapse_file(st
 	struct address_space *mapping = file->f_mapping;
 	struct page *dst;
 	struct folio *folio, *tmp, *new_folio;
+	unsigned long new_pfn = -1;
 	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
 	LIST_HEAD(pagelist);
 	XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);

@@ -2272,6 +2273,7 @@ static enum scan_result collapse_file(st
 	result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER);
 	if (result != SCAN_SUCCEED)
 		goto out;
+	new_pfn = folio_pfn(new_folio);
 
 	mapping_set_update(&xas, mapping);
 

@@ -2675,7 +2677,7 @@ rollback:
 	folio_put(new_folio);
 out:
 	VM_BUG_ON(!list_empty(&pagelist));
-	trace_mm_khugepaged_collapse_file(mm, new_folio, index, addr, is_shmem, file, HPAGE_PMD_NR, result);
+	trace_mm_khugepaged_collapse_file(mm, new_pfn, index, addr, is_shmem, file, HPAGE_PMD_NR, result);
 	return result;
 }

_

Patches currently in -mm which might be from [email protected] are