mm: conditionally write-lock VMA in free_pgtables

Normally free_pgtables needs to lock affected VMAs except for the case
when VMAs were isolated under VMA write-lock.  munmap() does just that,
isolating while holding appropriate locks and then downgrading mmap_lock
and dropping per-VMA locks before freeing page tables.  Add a parameter to
free_pgtables for such scenario.

Link: https://lkml.kernel.org/r/20230227173632.3292573-20-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index ec7e89cc0532..8ca78ae8bba7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -362,7 +362,7 @@ void free_pgd_range(struct mmu_gather *tlb,
 
 void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 		   struct vm_area_struct *vma, unsigned long floor,
-		   unsigned long ceiling)
+		   unsigned long ceiling, bool mm_wr_locked)
 {
 	MA_STATE(mas, mt, vma->vm_end, vma->vm_end);
 
@@ -380,6 +380,8 @@ void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 		 * Hide vma from rmap and truncate_pagecache before freeing
 		 * pgtables
 		 */
+		if (mm_wr_locked)
+			vma_start_write(vma);
 		unlink_anon_vmas(vma);
 		unlink_file_vma(vma);
 
@@ -394,6 +396,8 @@ void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 			       && !is_vm_hugetlb_page(next)) {
 				vma = next;
 				next = mas_find(&mas, ceiling - 1);
+				if (mm_wr_locked)
+					vma_start_write(vma);
 				unlink_anon_vmas(vma);
 				unlink_file_vma(vma);
 			}