percpu: cast percpu pointer in PERCPU_PTR() via unsigned long

Cast pointer from percpu address space to generic (kernel) address space
in PERCPU_PTR() macro via unsigned long intermediate cast [1].  This
intermediate cast is also required to avoid build failure when GCC's
strict named address space checks for x86 targets [2] are enabled.

Found by GCC's named address space checks.

[1] https://sparse.docs.kernel.org/en/latest/annotations.html#address-space-name
[2] https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html#x86-Named-Address-Spaces

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]>

include/linux/percpu-defs.h

@@ -221,7 +221,10 @@ do {									\
 } while (0)
 
 #define PERCPU_PTR(__p)							\
-	(typeof(*(__p)) __force __kernel *)(__p);
+({									\
+	unsigned long __pcpu_ptr = (__force unsigned long)(__p);	\
+	(typeof(*(__p)) __force __kernel *)(__pcpu_ptr);		\
+})
 
 #ifdef CONFIG_SMP