The main Tasks RCU quiescent state is voluntary context switch. However,
userspace execution is also a valid quiescent state, and is a valuable one
for userspace applications that spin repeatedly executing light-weight
non-sleeping system calls. Currently, such an application can delay a
Tasks RCU grace period for many tens of seconds.
This commit therefore enlists the aid of the scheduler-clock interrupt to
provide a Tasks RCU quiescent state when it interrupted a task executing
in userspace.
[ paulmck: Apply feedback from kernel test robot. ]
Cc: Martin KaFai Lau <kafai@xxxxxx>
Cc: Neil Spring <ntspring@xxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
include/linux/rcupdate.h | 1 +
kernel/rcu/tree.c | 2 ++
2 files changed, 3 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e7c39c200e2b..1a32036c918c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -196,6 +196,7 @@ void synchronize_rcu_tasks_rude(void);
void exit_tasks_rcu_start(void);
void exit_tasks_rcu_finish(void);
#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
#define rcu_tasks_qs(t, preempt) do { } while (0)
#define rcu_note_voluntary_context_switch(t) do { } while (0)
#define call_rcu_tasks call_rcu
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a4b8189455d5..8dbfb63f0391 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2624,6 +2624,8 @@ void rcu_sched_clock_irq(int user)
rcu_flavor_sched_clock_irq(user);
if (rcu_pending(user))
invoke_rcu_core();
+ if (user)
+ rcu_tasks_classic_qs(current, false);
lockdep_assert_irqs_disabled();
trace_rcu_utilization(TPS("End scheduler-tick"));
--
2.31.1.189.g2e36527f23
