From e611b0a9a274ab3f65647eafee410b5b6da56ea8 Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Mon, 23 May 2022 09:40:59 -0700 Subject: [PATCH] mm/mmap: prevent pagefault handler from racing with mmu_notifier registration Page fault handlers might need to fire MMU notifications while a new notifier is being registered. Modify mm_take_all_locks to write-lock all VMAs and prevent this race with fault handlers that would hold VMA locks. VMAs are locked before i_mmap_rwsem and anon_vma to keep the same locking order as in page fault handlers. Signed-off-by: Suren Baghdasaryan --- mm/mmap.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/mmap.c b/mm/mmap.c index 50f6494d2178d..5e2193f59a8d6 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3571,6 +3571,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping) * of mm/rmap.c: * - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for * hugetlb mapping); + * - all vmas marked locked * - all i_mmap_rwsem locks; * - all anon_vma->rwseml * @@ -3596,6 +3597,7 @@ int mm_take_all_locks(struct mm_struct *mm) mas_for_each(&mas, vma, ULONG_MAX) { if (signal_pending(current)) goto out_unlock; + vma_write_lock(vma); if (vma->vm_file && vma->vm_file->f_mapping && is_vm_hugetlb_page(vma)) vm_lock_mapping(mm, vma->vm_file->f_mapping); @@ -3682,6 +3684,7 @@ void mm_drop_all_locks(struct mm_struct *mm) if (vma->vm_file && vma->vm_file->f_mapping) vm_unlock_mapping(vma->vm_file->f_mapping); } + vma_write_unlock_mm(mm); mutex_unlock(&mm_all_locks_mutex); } -- 2.50.1