[079/117] powerpc: Reset kernel stack on cpu online from cede state

[Greg KH]

2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx>

commit 8dbce53cc249a76e9450708d291fce5a7e29c6a1 upstream.

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@xxxxxxxxxxxxxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/powerpc/kernel/head_64.S                   |   11 +++++++++++
 arch/powerpc/platforms/pseries/hotplug-cpu.c    |    9 ++++-----
 arch/powerpc/platforms/pseries/offline_states.h |    1 +
 3 files changed, 16 insertions(+), 5 deletions(-)

--- 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
 
 /*
--- 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) {
 
--- a/arch/powerpc/platforms/pseries/offline_states.h
+++ b/arch/powerpc/platforms/pseries/offline_states.h
@@ -35,4 +35,5 @@ static inline void set_default_offline_s
 
 extern enum cpu_state_vals get_preferred_offline_state(int cpu);
 extern int start_secondary(void);
+extern void start_secondary_resume(void);
 #endif


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