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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 May 2025 09:36:14.4955 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: aabdb723-f837-4755-c0a5-08dd99141877 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B36F.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ1PR12MB6170 Content-Type: text/plain; charset="utf-8" folio_mapcount() checks folio_test_large() before proceeding to folio_large_mapcount(), but there exists a race window where a folio could be split between these checks which triggered the VM_WARN_ON_FOLIO(!folio_test_large(folio), folio) in folio_large_mapcount(). Take a temporary folio reference in hpage_collapse_scan_file() to prevent races with concurrent folio splitting/freeing. This prevent potential incorrect large folio detection. Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@googl= e.com Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") Suggested-by: David Hildenbrand Signed-off-by: Shivank Garg --- mm/khugepaged.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index cc945c6ab3bd..6e8902f9d88c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2295,6 +2295,17 @@ static int hpage_collapse_scan_file(struct mm_struct= *mm, unsigned long addr, continue; } =20 + if (!folio_try_get(folio)) { + xas_reset(&xas); + continue; + } + + if (unlikely(folio !=3D xas_reload(&xas))) { + folio_put(folio); + xas_reset(&xas); + continue; + } + if (folio_order(folio) =3D=3D HPAGE_PMD_ORDER && folio->index =3D=3D start) { /* Maybe PMD-mapped */ @@ -2305,23 +2316,27 @@ static int hpage_collapse_scan_file(struct mm_struc= t *mm, unsigned long addr, * it's safe to skip LRU and refcount checks before * returning. */ + folio_put(folio); break; } =20 node =3D folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result =3D SCAN_SCAN_ABORT; + folio_put(folio); break; } cc->node_load[node]++; =20 if (!folio_test_lru(folio)) { result =3D SCAN_PAGE_LRU; + folio_put(folio); break; } =20 if (!is_refcount_suitable(folio)) { result =3D SCAN_PAGE_COUNT; + folio_put(folio); break; } =20 @@ -2333,6 +2348,7 @@ static int hpage_collapse_scan_file(struct mm_struct = *mm, unsigned long addr, */ =20 present +=3D folio_nr_pages(folio); + folio_put(folio); =20 if (need_resched()) { xas_pause(&xas); --=20 2.34.1