[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>

arch/powerpc/kernel/lparcfg.c

@@ -77,7 +77,7 @@ static int iseries_lparcfg_data(struct seq_file *m, void *v)
 	int processors, max_processors;
 	unsigned long purr = get_purr();
 
-	shared = (int)(get_lppaca()->shared_proc);
+	shared = (int)(local_paca->lppaca_ptr->shared_proc);
 
 	seq_printf(m, "system_active_processors=%d\n",
 		   (int)HvLpConfig_getSystemPhysicalProcessors());

include/asm-powerpc/io.h

@@ -86,7 +86,7 @@ extern unsigned long pci_dram_offset;
  */
 
 #ifdef CONFIG_PPC64
-#define IO_SET_SYNC_FLAG()	do { get_paca()->io_sync = 1; } while(0)
+#define IO_SET_SYNC_FLAG()	do { local_paca->io_sync = 1; } while(0)
 #else
 #define IO_SET_SYNC_FLAG()
 #endif

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)
 

include/asm-powerpc/percpu.h

@@ -28,7 +28,7 @@
 /* var is in discarded region: offset to particular copy we want */
 #define per_cpu(var, cpu) (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset(cpu)))
 #define __get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
-#define __raw_get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, __my_cpu_offset()))
+#define __raw_get_cpu_var(var) (*RELOC_HIDE(&per_cpu__##var, local_paca->data_offset))
 
 /* A macro to avoid #include hell... */
 #define percpu_modcopy(pcpudst, src, size)			\

include/asm-powerpc/smp.h

@@ -45,7 +45,7 @@ void generic_mach_cpu_die(void);
 #endif
 
 #ifdef CONFIG_PPC64
-#define raw_smp_processor_id()	(get_paca()->paca_index)
+#define raw_smp_processor_id()	(local_paca->paca_index)
 #define hard_smp_processor_id() (get_paca()->hw_cpu_id)
 #else
 /* 32-bit */

lib/Kconfig.debug

@@ -167,7 +167,7 @@ config SLUB_DEBUG_ON
 
 config DEBUG_PREEMPT
 	bool "Debug preemptible kernel"
-	depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
+	depends on DEBUG_KERNEL && PREEMPT && (TRACE_IRQFLAGS_SUPPORT || PPC64)
 	default y
 	help
 	  If you say Y here then the kernel will use a debug variant of the