The patch titled Subject: migrate: correct lock ordering for hugetlb file folios has been added to the -mm mm-hotfixes-unstable branch. Its filename is migrate-correct-lock-ordering-for-hugetlb-file-folios.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
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: "Matthew Wilcox (Oracle)" willy@infradead.org Subject: migrate: correct lock ordering for hugetlb file folios Date: Fri, 9 Jan 2026 04:13:42 +0000
Syzbot has found a deadlock (analyzed by Lance Yang):
1) Task (5749): Holds folio_lock, then tries to acquire i_mmap_rwsem(read lock). 2) Task (5754): Holds i_mmap_rwsem(write lock), then tries to acquire folio_lock.
migrate_pages() -> migrate_hugetlbs() -> unmap_and_move_huge_page() <- Takes folio_lock! -> remove_migration_ptes() -> __rmap_walk_file() -> i_mmap_lock_read() <- Waits for i_mmap_rwsem(read lock)!
hugetlbfs_fallocate() -> hugetlbfs_punch_hole() <- Takes i_mmap_rwsem(write lock)! -> hugetlbfs_zero_partial_page() -> filemap_lock_hugetlb_folio() -> filemap_lock_folio() -> __filemap_get_folio <- Waits for folio_lock!
The migration path is the one taking locks in the wrong order according to the documentation at the top of mm/rmap.c. So expand the scope of the existing i_mmap_lock to cover the calls to remove_migration_ptes() too.
This is (mostly) how it used to be after commit c0d0381ade79. That was removed by 336bf30eb765 for both file & anon hugetlb pages when it should only have been removed for anon hugetlb pages.
Link: https://lkml.kernel.org/r/20260109041345.3863089-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Fixes: 336bf30eb765 ("hugetlbfs: fix anon huge page migration race") Reported-by: syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/68e9715a.050a0220.1186a4.000d.GAE@google.com Debugged-by: Lance Yang lance.yang@linux.dev Acked-by: David Hildenbrand (Red Hat) david@kernel.org Acked-by: Zi Yan ziy@nvidia.com Cc: Alistair Popple apopple@nvidia.com Cc: Byungchul Park byungchul@sk.com Cc: Gregory Price gourry@gourry.net Cc: Jann Horn jannh@google.com Cc: Joshua Hahn joshua.hahnjy@gmail.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Matthew Brost matthew.brost@intel.com Cc: Rakie Kim rakie.kim@sk.com Cc: Rik van Riel riel@surriel.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Ying Huang ying.huang@linux.alibaba.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/migrate.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/mm/migrate.c~migrate-correct-lock-ordering-for-hugetlb-file-folios +++ a/mm/migrate.c @@ -1458,6 +1458,7 @@ static int unmap_and_move_huge_page(new_ int page_was_mapped = 0; struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; + enum ttu_flags ttu = 0;
if (folio_ref_count(src) == 1) { /* page was freed from under us. So we are done. */ @@ -1498,8 +1499,6 @@ static int unmap_and_move_huge_page(new_ goto put_anon;
if (folio_mapped(src)) { - enum ttu_flags ttu = 0; - if (!folio_test_anon(src)) { /* * In shared mappings, try_to_unmap could potentially @@ -1516,16 +1515,17 @@ static int unmap_and_move_huge_page(new_
try_to_migrate(src, ttu); page_was_mapped = 1; - - if (ttu & TTU_RMAP_LOCKED) - i_mmap_unlock_write(mapping); }
if (!folio_mapped(src)) rc = move_to_new_folio(dst, src, mode);
if (page_was_mapped) - remove_migration_ptes(src, !rc ? dst : src, 0); + remove_migration_ptes(src, !rc ? dst : src, + ttu ? RMP_LOCKED : 0); + + if (ttu & TTU_RMAP_LOCKED) + i_mmap_unlock_write(mapping);
unlock_put_anon: folio_unlock(dst); _
Patches currently in -mm which might be from willy@infradead.org are
migrate-correct-lock-ordering-for-hugetlb-file-folios.patch migrate-replace-rmp_-flags-with-ttu_-flags.patch