linux-kernel - [PATCH] userfaultfd: fix deadlock warning when locking src and dst VMAs

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Message-ID: <20240321235818.125118-1-lokeshgidra@google.com>
Date: Thu, 21 Mar 2024 16:58:18 -0700
From: Lokesh Gidra <lokeshgidra@...gle.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, surenb@...gle.com, 
	kernel-team@...roid.com, aarcange@...hat.com, peterx@...hat.com, 
	david@...hat.com, axelrasmussen@...gle.com, bgeffon@...gle.com, 
	jannh@...gle.com, kaleshsingh@...gle.com, ngeoffray@...gle.com, 
	rppt@...nel.org, hdanton@...a.com, Lokesh Gidra <lokeshgidra@...gle.com>, 
	syzbot+49056626fe41e01f2ba7@...kaller.appspotmail.com
Subject: [PATCH] userfaultfd: fix deadlock warning when locking src and dst VMAs

Use down_read_nested() to avoid the warning.

Reported-by: syzbot+49056626fe41e01f2ba7@...kaller.appspotmail.com
Signed-off-by: Lokesh Gidra <lokeshgidra@...gle.com>
---
 mm/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 712160cd41ec..3c3539c573e7 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1444,7 +1444,8 @@ static int uffd_move_lock(struct mm_struct *mm,
 		 */
 		down_read(&(*dst_vmap)->vm_lock->lock);
 		if (*dst_vmap != *src_vmap)
-			down_read(&(*src_vmap)->vm_lock->lock);
+			down_read_nested(&(*src_vmap)->vm_lock->lock,
+					 SINGLE_DEPTH_NESTING);
 	}
 	mmap_read_unlock(mm);
 	return err;
-- 
2.44.0.396.g6e790dbe36-goog