percpu: introduce PERCPU_PTR() macro

Introduce PERCPU_PTR() macro to cast the percpu pointer from the percpu
address space to a generic (kernel) address space.  Use it in
per_cpu_ptr() and related SHIFT_PERCPU_PTR() macros.

Also remove common knowledge from SHIFT_PERCPU_PTR() comment, "weird cast"
is just a standard way to inform sparse of a cast from the percpu address
space to a generic address space.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Uros Bizjak <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ubizjak

include/linux/percpu-defs.h

@@ -220,15 +220,17 @@ do {									\
 	(void)__vpp_verify;						\
 } while (0)
 
+#define PERCPU_PTR(__p)							\
+	(typeof(*(__p)) __force __kernel *)(__p);
+
 #ifdef CONFIG_SMP
 
 /*
- * Add an offset to a pointer but keep the pointer as-is.  Use RELOC_HIDE()
- * to prevent the compiler from making incorrect assumptions about the
- * pointer value.  The weird cast keeps both GCC and sparse happy.
+ * Add an offset to a pointer.  Use RELOC_HIDE() to prevent the compiler
+ * from making incorrect assumptions about the pointer value.
  */
 #define SHIFT_PERCPU_PTR(__p, __offset)					\
-	RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
+	RELOC_HIDE(PERCPU_PTR(__p), (__offset))
 
 #define per_cpu_ptr(ptr, cpu)						\
 ({									\
@@ -258,7 +260,7 @@ do {									\
 ({									\
 	(void)(cpu);							\
 	__verify_pcpu_ptr(ptr);						\
-	(typeof(*(ptr)) __kernel __force *)(ptr);			\
+	PERCPU_PTR(ptr);						\
 })
 
 #define raw_cpu_ptr(ptr)	per_cpu_ptr(ptr, 0)