ARM: SMP: wait for CPU to be marked active

When we bring a CPU online, we should wait for it to become active
before entering the idle thread, so we know that the scheduler and
thread migration is going to work.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 344e52b16c8c..e7f92a4321f3 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -318,9 +318,13 @@ asmlinkage void __cpuinit secondary_start_kernel(void)
         smp_store_cpu_info(cpu);
 
         /*
-         * OK, now it's safe to let the boot CPU continue
+         * OK, now it's safe to let the boot CPU continue.  Wait for
+         * the CPU migration code to notice that the CPU is online
+         * before we continue.
          */
         set_cpu_online(cpu, true);
+        while (!cpu_active(cpu))
+                cpu_relax();
 
         /*
          * OK, it's off to the idle thread for us