On Mon, May 18, 2009 at 02:59:52PM +0800, Lai Jiangshan wrote:

Paul E. McKenney wrote:

quoted

+void sched_expedited_wake(void *unused)
+{
+	mutex_lock(&__get_cpu_var(sched_expedited_done_mutex));
+	if (__get_cpu_var(sched_expedited_done_qs) ==
+	    SCHED_EXPEDITED_QS_DONE_QS) {
+		__get_cpu_var(sched_expedited_done_qs) =
+			SCHED_EXPEDITED_QS_NEED_QS;
+		wake_up(&__get_cpu_var(sched_expedited_qs_wq));
+	}
+	mutex_unlock(&__get_cpu_var(sched_expedited_done_mutex));
+}

[...]

quoted

+		get_online_cpus();
+		preempt_disable();
+		mycpu = smp_processor_id();
+		smp_call_function(sched_expedited_wake, NULL, 1);

sched_expedited_wake() calls mutex_lock() which may sleep?

Good eyes!  Fixing this and the failure to release this lock in
krcu_sched_expedited_percpu() allows it to survive 10 hours of
rcutorture running in parallel with onlining/offlining random CPUs.

And I think you have re-implement workqueue.

Hmmm...  I suppose I could use schedule_work(), though I am concerned
about interference from other work.  But I will give this some thought.

							Thanx, Paul