Subject: [RFC PATCH RESEND 14/28] mm: mark VMAs as locked before isolating them

From: Suren Baghdasaryan <[email-masked]>
Date: Thu, 1 Sep 2022 10:35:02 -0700

Mark VMAs as locked before isolating them and clear their tree node so
that isolated VMAs are easily identifiable. In the later patches page
fault handlers will try locking the found VMA and will check whether
the VMA was isolated. Locking VMAs before isolating them ensures that
page fault handlers don't operate on isolated VMAs.

Signed-off-by: Suren Baghdasaryan <[email-masked]>
---
 mm/mmap.c  | 2 ++
 mm/nommu.c | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 094678b4434b..b0d78bdc0de0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -421,12 +421,14 @@ static inline void vma_rb_insert(struct vm_area_struct *vma,
 
 static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
 {
+	vma_mark_locked(vma);
 	/*
 	 * Note rb_erase_augmented is a fairly large inline function,
 	 * so make sure we instantiate it only once with our desired
 	 * augmented rbtree callbacks.
 	 */
 	rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
+	RB_CLEAR_NODE(&vma->vm_rb);
 }
 
 static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
diff --git a/mm/nommu.c b/mm/nommu.c
index e819cbc21b39..ff9933e57501 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -622,6 +622,7 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
 	struct mm_struct *mm = vma->vm_mm;
 	struct task_struct *curr = current;
 
+	vma_mark_locked(vma);
 	mm->map_count--;
 	for (i = 0; i < VMACACHE_SIZE; i++) {
 		/* if the vma is cached, invalidate the entire cache */
@@ -644,6 +645,7 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
 
 	/* remove from the MM's tree and list */
 	rb_erase(&vma->vm_rb, &mm->mm_rb);
+	RB_CLEAR_NODE(&vma->vm_rb);
 
 	__vma_unlink_list(mm, vma);
 }
-- 
2.37.2.789.g6183377224-goog