+ mm-khugepaged-dont-map-folios-that-are-not-uptodate-in-madv_collapse.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm/khugepaged: don't map folios that are not uptodate in MADV_COLLAPSE
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-khugepaged-dont-map-folios-that-are-not-uptodate-in-madv_collapse.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-dont-map-folios-that-are-not-uptodate-in-madv_collapse.patch

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

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------------------------------------------------------
From: "David Hildenbrand (Arm)" <david@kernel.org>
Subject: mm/khugepaged: don't map folios that are not uptodate in MADV_COLLAPSE
Date: Thu, 05 Nov 2026 19:16:44 +0100

madvise(MADV_COLLAPSE) can map PMD-sized pagecache folios that are not
uptodate.  For example, shmem fallocate() can put such folios into the
page cache.

collapse_file() already refuses to proceed with folios that are not
uptodate.  Let's just do the same in try_collapse_pte_mapped_thp() and
skip such folios, leaving handling to the page faults.

Note that collapse_file() effectively clears shmem folios through
shmem_get_folio(); let's keep this fix simple and simply let the page
fault path deal with that.

Link: https://lore.kernel.org/20261105-set_huge_pmd_uptodate-v1-1-a78d8a1b7117@kernel.org
Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Chris Mason <mason@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Zach O'Keefe <zokeefe@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: <stable@vger.kernel.org>
---

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

--- a/mm/khugepaged.c~mm-khugepaged-dont-map-folios-that-are-not-uptodate-in-madv_collapse
+++ a/mm/khugepaged.c
@@ -1888,6 +1888,12 @@ static enum scan_result try_collapse_pte
 		goto drop_folio;
 	}
 
+	/* Leave any uninitialized folios to the page fault path. */
+	if (!folio_test_uptodate(folio)) {
+		result = SCAN_FAIL;
+		goto drop_folio;
+	}
+
 	result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
 	switch (result) {
 	case SCAN_SUCCEED:
_

Patches currently in -mm which might be from david@kernel.org are

mm-memory-failure-fix-folio-refcount-leak-and-min_order_for_split-locking.patch
mm-khugepaged-dont-map-folios-that-are-not-uptodate-in-madv_collapse.patch