diff --git a/mm/mmap.c b/mm/mmap.c
index 9800e29..52f6c6b1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2639,13 +2639,6 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 	if (vma->vm_start >= end)
 		return 0;
 
-	if (uf) {
-		int error = userfaultfd_unmap_prep(vma, start, end, uf);
-
-		if (error)
-			return error;
-	}
-
 	/*
 	 * If we need to split any vma, do it now to save pain later.
 	 *
@@ -2679,6 +2672,21 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 	}
 	vma = prev ? prev->vm_next : mm->mmap;
 
+	if (unlikely(uf)) {
+		/*
+		 * If userfaultfd_unmap_prep returns an error the vmas
+		 * will remain splitted, but userland will get a
+		 * highly unexpected error anyway. This is no
+		 * different than the case where the first of the two
+		 * __split_vma fails, but we don't undo the first
+		 * split, despite we could. This is unlikely enough
+		 * failure that it's not worth optimizing it for.
+		 */
+		int error = userfaultfd_unmap_prep(vma, start, end, uf);
+		if (error)
+			return error;
+	}
+
 	/*
 	 * unlock any mlock()ed ranges before detaching vmas
 	 */