[PATCH] powerpc: reset kernel stack on cpu online from cede state

[Vaidyanathan Srinivasan]

    	powerpc: reset kernel stack on cpu online from cede state
    
    	Cpu hotplug (offline) without dlpar operation will place cpu
    	in cede state and the extended_cede_processor() function will
    	return when resumed.
    
    	Kernel stack pointer needs to be reset before
    	start_secondary() is called to continue the online operation.
    
    	Added new function start_secondary_resume() to do the above
    	steps.
    
Signed-off-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 9258074..567cd57 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -615,6 +615,17 @@ _GLOBAL(start_secondary_prolog)
 	std	r3,0(r1)		/* Zero the stack frame pointer	*/
 	bl	.start_secondary
 	b	.
+/*
+ * Reset stack pointer and call start_secondary
+ * to continue with online operation when woken up
+ * from cede in cpu offline.
+ */
+_GLOBAL(start_secondary_resume)
+	ld	r1,PACAKSAVE(r13)	/* Reload kernel stack pointer */
+	li	r3,0
+	std	r3,0(r1)		/* Zero the stack frame pointer	*/
+	bl	.start_secondary
+	b	.
 #endif
 
 /*
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index 6ea4698..9be7af4 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -146,12 +146,11 @@ static void pseries_mach_cpu_die(void)
 		unregister_slb_shadow(hwcpu, __pa(get_slb_shadow()));
 
 		/*
-		 * NOTE: Calling start_secondary() here for now to
-		 * start new context.
-		 * However, need to do it cleanly by resetting the
-		 * stack pointer.
+		 * Call to start_secondary_resume() will not return.
+		 * Kernel stack will be reset and start_secondary()
+		 * will be called to continue the online operation.
 		 */
-		start_secondary();
+		start_secondary_resume();
 
 	} else if (get_preferred_offline_state(cpu) == CPU_STATE_OFFLINE) {
 
diff --git a/arch/powerpc/platforms/pseries/offline_states.h b/arch/powerpc/platforms/pseries/offline_states.h
index 22574e0..da07256 100644
--- a/arch/powerpc/platforms/pseries/offline_states.h
+++ b/arch/powerpc/platforms/pseries/offline_states.h
@@ -14,5 +14,5 @@ extern void set_cpu_current_state(int cpu, enum cpu_state_vals state);
 extern enum cpu_state_vals get_preferred_offline_state(int cpu);
 extern void set_preferred_offline_state(int cpu, enum cpu_state_vals state);
 extern void set_default_offline_state(int cpu);
-extern int start_secondary(void);
+extern void start_secondary_resume(void);
 #endif