linux-kernel - [PATCH tip/core/rcu 02/27] rcu: Improve rcu_note_voluntary_context

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Date:   Mon, 25 Jun 2018 17:34:48 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Byungchul Park <byungchul.park@....com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 02/27] rcu: Improve rcu_note_voluntary_context_switch() reporting

From: Byungchul Park <byungchul.park@....com>

We expect a quiescent state of TASKS_RCU when cond_resched_tasks_rcu_qs()
is called, no matter whether it actually be scheduled or not. However,
it currently doesn't report the quiescent state when the task enters
into __schedule() as it's called with preempt = true. So make it report
the quiescent state unconditionally when cond_resched_tasks_rcu_qs() is
called.

And in TINY_RCU, even though the quiescent state of rcu_bh also should
be reported when the tick interrupt comes from user, it doesn't. So make
it reported.

Lastly in TREE_RCU, rcu_note_voluntary_context_switch() should be
reported when the tick interrupt comes from not only user but also idle,
as an extended quiescent state.

Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
[ paulmck: Simplify rcutiny portion given no RCU-tasks for !PREEMPT. ]
---
 include/linux/rcupdate.h | 4 ++--
 kernel/rcu/tiny.c        | 4 +---
 kernel/rcu/tree.c        | 4 ++--
 3 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 67ec077c7ee5..5cab15e7ec83 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -194,8 +194,8 @@ static inline void exit_tasks_rcu_finish(void) { }
  */
 #define cond_resched_tasks_rcu_qs() \
 do { \
-	if (!cond_resched()) \
-		rcu_note_voluntary_context_switch_lite(current); \
+	rcu_note_voluntary_context_switch_lite(current); \
+	cond_resched(); \
 } while (0)
 
 /*
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index a64eee0db39e..befc9321a89c 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -122,10 +122,8 @@ void rcu_check_callbacks(int user)
 {
 	if (user)
 		rcu_sched_qs();
-	else if (!in_softirq())
+	if (user || !in_softirq())
 		rcu_bh_qs();
-	if (user)
-		rcu_note_voluntary_context_switch(current);
 }
 
 /*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4b0aee4f9318..50a8f49e1763 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2645,6 +2645,7 @@ void rcu_check_callbacks(int user)
 
 		rcu_sched_qs();
 		rcu_bh_qs();
+		rcu_note_voluntary_context_switch(current);
 
 	} else if (!in_softirq()) {
 
@@ -2660,8 +2661,7 @@ void rcu_check_callbacks(int user)
 	rcu_preempt_check_callbacks();
 	if (rcu_pending())
 		invoke_rcu_core();
-	if (user)
-		rcu_note_voluntary_context_switch(current);
+
 	trace_rcu_utilization(TPS("End scheduler-tick"));
 }
 
-- 
2.17.1