7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik [ Upstream commit d42032c0fe3ca007986c1229128775af0340fbec ] Since commit bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") the lock of a private hugetlb VMA that owns a reservation is the rw_sema of its resv_map. The hugetlb_vma_*lock*() helpers find it through vma->vm_private_data, anew for every lock and every unlock. At the end of mremap() the old VMA has to let go of the resv_map, which now belongs to the new VMA: clear_vma_resv_huge_pages() stores NULL into vm_private_data. mremap() holds mmap_lock for writing and has write locked the VMA, which keeps away everybody who comes through the mm. It does not keep away those who find the VMA through the file. For hole punch and truncation hugetlb_vmdelete_list() does hugetlb_vma_trylock_write(vma); locks resv_map->rw_sema unmap_hugepage_range(vma, ...); vm_private_data = NULL hugetlb_vma_unlock_write(vma); no resv_map: does nothing and the rw_sema stays write locked for ever: WARNING: lock held when returning to user space! mremap_punch/116 is leaving the kernel with locks still held! locks held by mremap_punch/116: 1, last CPU#1: #0: (&resv_map->rw_sema){+.+.}-{4:4}, at: hugetlb_vmdelete_list+0x46/0x160 The next fault in the new VMA sleeps in hugetlb_vma_lock_read(), uninterruptibly, and it holds its entry of hugetlb_fault_mutex_table[]. That table is global, so a fault of any other process on a page that hashes to the same entry sleeps uninterruptibly as well. All those who take the lock of a private VMA without taking the mmap/vma lock are affected: rmap walks. So hold i_mmap_rwsem around the clearing of the resv_map. No change of behaviour, other than that mremap() of a hugetlb VMA takes i_mmap_rwsem once more. Original fix generated by an LLM and sent in private by Josef. [david: avoid local variable, move and refine comment, description cleanups+simplifications] Link: https://lore.kernel.org/20261015-urgent_fixes-v1-5-42796911043b@kernel.org Fixes: bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") Signed-off-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Andrew Morton Reported-by: Chris Mason Reviewed-by: Lorenzo Stoakes (ARM) Acked-by: Muchun Song Reviewed-by: Lance Yang Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Pedro Falcato Cc: Oscar Salvador Cc: Miaohe Lin Cc: Naoya Horiguchi Cc: Adam Litke Cc: Mel Gorman Cc: Rik van Riel Cc: Peter Xu Cc: Kiryl Shutsemau Cc: Mike Rapoport Cc: Signed-off-by: Sasha Levin --- mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 061bdd61f2ad9..fb7205c703b3f 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7473,6 +7473,15 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) */ void fixup_hugetlb_reservations(struct vm_area_struct *vma) { - if (is_vm_hugetlb_page(vma)) - clear_vma_resv_huge_pages(vma); + if (!is_vm_hugetlb_page(vma)) + return; + + /* + * Rmap walks might still find this VMA and take the lock + * inside the reservation map for __vma_private_lock(). Don't clear + * the reservation map while that is possible. + */ + i_mmap_lock_write(vma->vm_file->f_mapping); + clear_vma_resv_huge_pages(vma); + i_mmap_unlock_write(vma->vm_file->f_mapping); } -- 2.53.0