[PATCH 6.6.y] mm/mempolicy: fix wrong mmap_read_unlock() in migrate_to_node()

["David Hildenbrand (Arm)" <david@kernel.org>]

The backport of commit 091c1dd2d4df ("mm/mempolicy: fix migrate_to_node()
assuming there is at least one VMA in a MM") contains an error:
migrate_to_node() does not lock the mmap_lock itself, that is handled by
the caller instead.

So let's drop the wrong mmap_read_unlock(). Fortunately, this path is
very hard to hit in practice.

Fixes: a13b2b9b0b0b ("mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM")
Reported-by: Li Ying <liying3@sungrowpower.com>
Closes: https://lore.kernel.org/r/aaZgUNxAyKC2IwuG@casper.infradead.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/mempolicy.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 94c74c594d10..d8007e1c2690 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1071,10 +1071,8 @@ static long migrate_to_node(struct mm_struct *mm, int source, int dest,
 
 	VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
 	vma = find_vma(mm, 0);
-	if (unlikely(!vma)) {
-		mmap_read_unlock(mm);
+	if (unlikely(!vma))
 		return 0;
-	}
 
 	/*
 	 * This does not migrate the range, but isolates all pages that
-- 
2.43.0