[PATCH] rcu-tasks: Avoid rtp_irq_work triggering when the rcu-tasks GP is ongoing

[Zqiang]

This commit generate rcu_task_gp_in_progress() to check whether
the rcu-tasks GP is ongoing, if is ongoing, avoid trigger
rtp_irq_work to wakeup rcu tasks kthreads in call_rcu_tasks_generic().

The test results are as follows:

echo call_rcu_tasks_iw_wakeup > /sys/kernel/debug/tracing/set_ftrace_filter
echo 1 > /sys/kernel/debug/tracing/function_profile_enabled
insmod rcutorture.ko torture_type=tasks-tracing fwd_progress=4
sleep 600
rmmod rcutorture.ko
echo 0 > /sys/kernel/debug/tracing/function_profile_enabled
echo > /sys/kernel/debug/tracing/set_ftrace_filter

head /sys/kernel/debug/tracing/trace_stat/function*

original: 56376  apply patch: 33521

Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
---
 
original:
==> /sys/kernel/debug/tracing/trace_stat/function0 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup             13217    19292.52 us     1.459 us        8.834 us    

==> /sys/kernel/debug/tracing/trace_stat/function1 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup             15146    22377.01 us     1.477 us        22.873 us   

==> /sys/kernel/debug/tracing/trace_stat/function2 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup             12561    18125.76 us     1.443 us        6.372 us    

==> /sys/kernel/debug/tracing/trace_stat/function3 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup             15452    21770.57 us     1.408 us        6.710 us

apply patch:
==> /sys/kernel/debug/tracing/trace_stat/function0 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup              8334    15121.13 us     1.814 us        4.457 us    

==> /sys/kernel/debug/tracing/trace_stat/function1 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup              8355    15760.51 us     1.886 us        14.775 us   

==> /sys/kernel/debug/tracing/trace_stat/function2 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup              7219    14194.27 us     1.966 us        42.440 us   

==> /sys/kernel/debug/tracing/trace_stat/function3 <==
  Function                               Hit    Time            Avg             s^2
  --------                               ---    ----            ---             ---
  call_rcu_tasks_iw_wakeup              9613    19850.04 us     2.064 us        91.023 us  

 kernel/rcu/tasks.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 147b5945d67a..36c7e1d441d0 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -317,6 +317,11 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
 	rcuwait_wake_up(&rtp->cbs_wait);
 }
 
+static int rcu_task_gp_in_progress(struct rcu_tasks *rtp)
+{
+	return rcu_seq_state(rcu_seq_current(&rtp->tasks_gp_seq));
+}
+
 // Enqueue a callback for the specified flavor of Tasks RCU.
 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 				   struct rcu_tasks *rtp)
@@ -375,7 +380,8 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	}
 	rcu_read_unlock();
 	/* We can't create the thread unless interrupts are enabled. */
-	if (needwake && READ_ONCE(rtp->kthread_ptr))
+	if (needwake && READ_ONCE(rtp->kthread_ptr) &&
+			!rcu_task_gp_in_progress(rtp))
 		irq_work_queue(&rtpcp->rtp_irq_work);
 }
 
-- 
2.17.1