rcu: Improve rcu_note_voluntary_context_switch() reporting

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@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Simplify rcutiny portion given no RCU-tasks for !PREEMPT. ]

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 67ec077..5cab15e 100644 (file)
--- 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 a64eee0..befc932 100644 (file)
--- 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 d3333ee..19beabe 100644 (file)
--- 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"));
 }