x86: cpu-hotplug: Prevent softirq wakeup on wrong CPU

[pandora-kernel.git] / arch / x86 / kernel / smpboot.c

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 33a0c11..9fd3137 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -285,6 +285,19 @@ notrace static void __cpuinit start_secondary(void *unused)
        per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
        x86_platform.nmi_init();
 
+       /*
+        * Wait until the cpu which brought this one up marked it
+        * online before enabling interrupts. If we don't do that then
+        * we can end up waking up the softirq thread before this cpu
+        * reached the active state, which makes the scheduler unhappy
+        * and schedule the softirq thread on the wrong cpu. This is
+        * only observable with forced threaded interrupts, but in
+        * theory it could also happen w/o them. It's just way harder
+        * to achieve.
+        */
+       while (!cpumask_test_cpu(smp_processor_id(), cpu_active_mask))
+               cpu_relax();
+
        /* enable local interrupts */
        local_irq_enable();