[PATCH 16/48] ftrace: Choose RCU Tasks based on TASKS_RCU rather than PREEMPTION

[Uladzislau Rezki (Sony)]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

The advent of CONFIG_PREEMPT_AUTO, AKA lazy preemption, will mean that
even kernels built with CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY
might see the occasional preemption, and that this preemption just might
happen within a trampoline.

Therefore, update ftrace_shutdown() to invoke synchronize_rcu_tasks()
based on CONFIG_TASKS_RCU instead of CONFIG_PREEMPTION.

[ paulmck: Apply Steven Rostedt feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: <linux-trace-kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
 kernel/trace/ftrace.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index da1710499698..6c96b30f3d63 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3157,8 +3157,7 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
 		 * synchronize_rcu_tasks() will wait for those tasks to
 		 * execute and either schedule voluntarily or enter user space.
 		 */
-		if (IS_ENABLED(CONFIG_PREEMPTION))
-			synchronize_rcu_tasks();
+		synchronize_rcu_tasks();
 
 		ftrace_trampoline_free(ops);
 	}
-- 
2.39.2