percpu: make accessors check for percpu pointer in sparse

The previous patch made sparse warn about percpu variables being used
directly without going through percpu accessors.  This patch
implements the other half - checking whether non percpu variable is
passed into percpu accessors.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index fded453..04f91c2 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -42,8 +42,10 @@
  */
 #ifndef SHIFT_PERCPU_PTR
 /* Weird cast keeps both GCC and sparse happy. */
-#define SHIFT_PERCPU_PTR(__p, __offset)				\
-	RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
+#define SHIFT_PERCPU_PTR(__p, __offset)	({				\
+	__verify_pcpu_ptr((__p));					\
+	RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset)); \
+})
 #endif
 
 /*