powerpc/smp: soft-replugged CPUs must go back to start_secondary

Various thing are torn down when a CPU is hot-unplugged. That CPU
is expected to go back to start_secondary when re-plugged to re
initialize everything, such as clock sources, maps, ...

Some implementations just return from cpu_die() callback
in the idle loop when the CPU is "re-plugged". This is not enough.

We fix it using a little asm trampoline which resets the stack
and calls back into start_secondary as if we were all fresh from
boot. The trampoline already existed on ppc64, but we add it for
ppc32

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

4 files changed, 17 insertions, 4 deletions

diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 66e237bbe15f..1de0e97a394f 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -36,6 +36,7 @@ extern void cpu_die(void);
 
 extern void smp_send_debugger_break(int cpu);
 extern void smp_message_recv(int);
+extern void start_secondary_resume(void);
 
 DECLARE_PER_CPU(unsigned int, cpu_pvr);
 
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 98c4b29a56f4..c5c24beb8387 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -890,6 +890,15 @@ __secondary_start:
         mtspr   SPRN_SRR1,r4
         SYNC
         RFI
+
+_GLOBAL(start_secondary_resume)
+        /* Reset stack */
+        rlwinm  r1,r1,0,0,(31-THREAD_SHIFT)     /* current_thread_info() */
+        addi    r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+        li      r3,0
+        std     r3,0(r1)                /* Zero the stack frame pointer */
+        bl      start_secondary
+        b       .
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_KVM_BOOK3S_HANDLER
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 981360509172..1c9956c43801 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -502,7 +502,7 @@ static struct device_node *cpu_to_l2cache(int cpu)
 }
 
 /* Activate a secondary processor. */
-int __devinit start_secondary(void *unused)
+void __devinit start_secondary(void *unused)
 {
         unsigned int cpu = smp_processor_id();
         struct device_node *l2_cache;
@@ -558,7 +558,8 @@ int __devinit start_secondary(void *unused)
         local_irq_enable();
 
         cpu_idle();
-        return 0;
+
+        BUG();
 }
 
 int setup_profiling_timer(unsigned int multiplier)
@@ -660,5 +661,9 @@ void cpu_die(void)
 {
         if (ppc_md.cpu_die)
                 ppc_md.cpu_die();
+
+        /* If we return, we re-enter start_secondary */
+        start_secondary_resume();
 }
+
 #endif
diff --git a/arch/powerpc/platforms/pseries/offline_states.h b/arch/powerpc/platforms/pseries/offline_states.h
index 75a6f480d931..08672d9136ab 100644
--- a/arch/powerpc/platforms/pseries/offline_states.h
+++ b/arch/powerpc/platforms/pseries/offline_states.h
@@ -34,6 +34,4 @@ static inline void set_default_offline_state(int cpu)
 #endif
 
 extern enum cpu_state_vals get_preferred_offline_state(int cpu);
-extern int start_secondary(void);
-extern void start_secondary_resume(void);
 #endif