Re: [PATCH v8 45/70] userfaultfd: use maple tree iterator to iterate VMAs

[Liam Howlett]

Andrew,

Please add this fix to your branch.

Thanks,
Liam
From 9ed858e47c3938fdff8c22fb386bdc3366773093 Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Date: Wed, 27 Apr 2022 11:13:03 -0400
Subject: [PATCH] fs/userfaultfd: Fix maple state in userfaultfd_register()

When VMAs are split/merged, the maple tree node may be replaced.
Re-walk the tree in such cases by calling mas_pause().

Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 fs/userfaultfd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index bb7338391b2c..974e04c51954 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1437,6 +1437,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 				 ((struct vm_userfaultfd_ctx){ ctx }),
 				 anon_vma_name(vma));
 		if (prev) {
+			/* vma_merge() invalidated the mas */
+			mas_pause(&mas);
 			vma = prev;
 			goto next;
 		}
@@ -1444,11 +1446,15 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 			ret = split_vma(mm, vma, start, 1);
 			if (ret)
 				break;
+			/* split_vma() invalidated the mas */
+			mas_pause(&mas);
 		}
 		if (vma->vm_end > end) {
 			ret = split_vma(mm, vma, end, 0);
 			if (ret)
 				break;
+			/* split_vma() invalidated the mas */
+			mas_pause(&mas);
 		}
 	next:
 		/*
-- 
2.35.1