percpu: fix DEBUG_PREEMPT per_cpu checking

2.6.25-rc1 percpu changes broke CONFIG_DEBUG_PREEMPT's per_cpu checking
on several architectures. On s390, sparc64 and x86 it's been weakened to
not checking at all; whereas on powerpc64 it's become too strict, issuing
warnings from __raw_get_cpu_var in io_schedule and init_timer for example.

Fix this by weakening powerpc's __my_cpu_offset to use the non-checking
local_paca instead of get_paca (which itself contains such a check);
and strengthening the generic my_cpu_offset to go the old slow way via
smp_processor_id when CONFIG_DEBUG_PREEMPT (debug_smp_processor_id is
where all the knowledge of what's correct when lives).

Signed-off-by: Hugh Dickins <[e-mail]>
Reviewed-by: Mike Travis <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/asm-generic/percpu.h

···
  */
 #ifndef __my_cpu_offset
 #define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
+#endif
+#ifdef CONFIG_DEBUG_PREEMPT
 #define my_cpu_offset per_cpu_offset(smp_processor_id())
 #else
 #define my_cpu_offset __my_cpu_offset

include/asm-powerpc/percpu.h

···
 #include <asm/paca.h>
 
 #define __per_cpu_offset(cpu) (paca[cpu].data_offset)
-#define __my_cpu_offset get_paca()->data_offset
+#define __my_cpu_offset local_paca->data_offset
 #define per_cpu_offset(x) (__per_cpu_offset(x))
 
 #endif /* CONFIG_SMP */