Date:   Fri, 27 Jan 2023 11:40:57 -0800
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Subject: [PATCH v2 20/33] mm/mmap: write-lock adjacent VMAs if they can grow
 into unmapped area
From:   Suren Baghdasaryan <surenb@google.com>
To:     akpm@linux-foundation.org
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Precedence: bulk

While unmapping VMAs, adjacent VMAs might be able to grow into the area
being unmapped. In such cases write-lock adjacent VMAs to prevent this
growth.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/mmap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 57cb3a2ac9b1..3baf218836bb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2399,11 +2399,13 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	 * down_read(mmap_lock) and collide with the VMA we are about to unmap.
 	 */
 	if (downgrade) {
-		if (next && (next->vm_flags & VM_GROWSDOWN))
+		if (next && (next->vm_flags & VM_GROWSDOWN)) {
+			vma_start_write(next);
 			downgrade = false;
-		else if (prev && (prev->vm_flags & VM_GROWSUP))
+		} else if (prev && (prev->vm_flags & VM_GROWSUP)) {
+			vma_start_write(prev);
 			downgrade = false;
-		else
+		} else
 			mmap_write_downgrade(mm);
 	}
 
-- 
2.39.1