From 5d90070816534882b9158f14154b7e2cdef1194a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 4 Mar 2022 10:41:44 -0800 Subject: [PATCH] rcu-tasks: Make Tasks RCU account for userspace execution 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 Cc: Neil Spring Signed-off-by: Paul E. McKenney --- 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"));