[PATCH v3] rcu-tasks: Make RCU Tasks Trace checking for userspace execution

[Zqiang]

For RCU tasks trace, the userspace execution is also a valid quiescent
state, when scheduling-clock interrupt handler interrupts the task is
in userspace. 

if the ->trc_reader_nesting is zero, and the ->trc_reader_special.b.need_qs
is not set, set the tasks ->trc_reader_special.b.need_qs is
TRC_NEED_QS_CHECKED, this cause grace-period kthread remove it from holdout
list if it remains here.

If the ->trc_reader_nesting is not zero(if one of the functions in the
scheduling-clock interrupt handler were traced/instrumented), and starts a
new RCU tasks trace grace period, when grace period kthread scan running
tasks on each CPU, this running uasks will be inserted into hold list.

This commit add rcu_tasks_trace_qs() to rcu_flavor_sched_clock_irq()
when the kernel built with no PREEMPT_RCU.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 v1->v2:
 Fix build error due to undeclared rcu_tasks_trace_qs(), note in no-PREEMPT_RCU
 kernel, the RCU Tasks is replaced by RCU, so rcu_note_voluntary_context_switch()
 only include rcu_tasks_trace_qs().
 
 v2->v3:
 Modify commit information.

 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 4152816dd29f..5fb0b2dd24fd 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -976,7 +976,7 @@ static void rcu_flavor_sched_clock_irq(int user)
 		 * neither access nor modify, at least not while the
 		 * corresponding CPU is online.
 		 */
-
+		rcu_note_voluntary_context_switch(current);
 		rcu_qs();
 	}
 }
-- 
2.25.1