[POWERPC] ppc64: support CONFIG_DEBUG_PREEMPT

Add CONFIG_DEBUG_PREEMPT support to ppc64: it was useful for testing
get_paca() preemption.  Cheat a little, just use debug_smp_processor_id()
in the debug version of get_paca(): it contains all the right checks and
reporting, though get_paca() doesn't really use smp_processor_id().

Use local_paca for what might have been called __raw_get_paca().
Silence harmless warnings from io.h and lparcfg.c with local_paca -
it is okay for iseries_lparcfg_data to be referencing shared_proc
with preemption enabled: all cpus should show the same value for
shared_proc.

Why do other architectures need TRACE_IRQFLAGS_SUPPORT for DEBUG_PREEMPT?
I don't know, ppc64 appears to get along fine without it.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/asm-powerpc/paca.h b/include/asm-powerpc/paca.h
index c6a5b1735666..fcd7b428ed0b 100644
--- a/include/asm-powerpc/paca.h
+++ b/include/asm-powerpc/paca.h
@@ -21,7 +21,18 @@
 #include        <asm/mmu.h>
 
 register struct paca_struct *local_paca asm("r13");
+
+#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
+extern unsigned int debug_smp_processor_id(void); /* from linux/smp.h */
+/*
+ * Add standard checks that preemption cannot occur when using get_paca():
+ * otherwise the paca_struct it points to may be the wrong one just after.
+ */
+#define get_paca()      ((void) debug_smp_processor_id(), local_paca)
+#else
 #define get_paca()      local_paca
+#endif
+
 #define get_lppaca()    (get_paca()->lppaca_ptr)
 #define get_slb_shadow()        (get_paca()->slb_shadow_ptr)