[PATCH 14/48] tracing: Select new NEED_TASKS_RCU Kconfig option

[PATCH 14/48] tracing: Select new NEED_TASKS_RCU Kconfig option

[Uladzislau Rezki (Sony)]

From: "Paul E. McKenney" <paulmck@kernel.org>

Currently, if a Kconfig option depends on TASKS_RCU, it conditionally does
"select TASKS_RCU if PREEMPTION".  This works, but requires any change in
this enablement logic to be replicated across all such "select" clauses.
A new NEED_TASKS_RCU Kconfig option has been created to allow this
enablement logic to be in one place in kernel/rcu/Kconfig.

Therefore, select the new NEED_TASKS_RCU Kconfig option instead of the
old TASKS_RCU option.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: <linux-trace-kernel@vger.kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/trace/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 61c541c36596..6cdc5ff919b0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -163,7 +163,7 @@ config TRACING
 	select BINARY_PRINTF
 	select EVENT_TRACING
 	select TRACE_CLOCK
-	select TASKS_RCU if PREEMPTION
+	select NEED_TASKS_RCU
 
 config GENERIC_TRACER
 	bool
@@ -204,7 +204,7 @@ config FUNCTION_TRACER
 	select GENERIC_TRACER
 	select CONTEXT_SWITCH_TRACER
 	select GLOB
-	select TASKS_RCU if PREEMPTION
+	select NEED_TASKS_RCU
 	select TASKS_RUDE_RCU
 	help
 	  Enable the kernel to trace every kernel function. This is done
-- 
2.39.2

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

[Uladzislau Rezki (Sony)]

From: "Paul E. McKenney" <paulmck@kernel.org>

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@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <linux-trace-kernel@vger.kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 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