[PATCH RT] smp: Wake ksoftirqd on PREEMPT_RT instead do_softirq().

[Sebastian Andrzej Siewior]

The softirq implementation on PREEMPT_RT does not provide do_softirq().
The other user of do_softirq() is replaced with a local_bh_disable()
+ enable() around the possible raise-softirq invocation. This can not be
done here because migration_cpu_stop() is invoked with disabled
preemption.

Wake the softirq thread on PREEMPT_RT if there are any pending softirqs.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
 kernel/smp.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -450,8 +450,18 @@ void flush_smp_call_function_from_idle(v
 
        local_irq_save(flags);
        flush_smp_call_function_queue(true);
-       if (local_softirq_pending())
-               do_softirq();
+
+       if (local_softirq_pending()) {
+
+               if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+                       do_softirq();
+               } else {
+                       struct task_struct *ksoftirqd = this_cpu_ksoftirqd();
+
+                       if (ksoftirqd && ksoftirqd->state != TASK_RUNNING)
+                               wake_up_process(ksoftirqd);
+               }
+       }
 
        local_irq_restore(flags);
 }