percpu: Make __verify_pcu_ptr handle per cpu pointers to arrays

__verify_pcpu_ptr() will cause a compilation failure if the type of the
pointer is a pointer to a fixed array of objects. Adding zero to the
pointer converts the type of pointer to that pointing to a single
object of the array.
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/percpu-defs.h

@@ -22,9 +22,12 @@
  * Macro which verifies @ptr is a percpu pointer without evaluating
  * @ptr.  This is to be used in percpu accessors to verify that the
  * input parameter is a percpu pointer.
+ *
+ * + 0 is required in order to convert the pointer type from a
+ * potential array type to a pointer to a single item of the array.
  */
 #define __verify_pcpu_ptr(ptr)	do {					\
-	const void __percpu *__vpp_verify = (typeof(ptr))NULL;		\
+	const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;	\
 	(void)__vpp_verify;						\
 } while (0)