On Wed, Feb 28, 2024 at 03:22:36PM -0500, Steven Rostedt wrote:
> On Wed, 28 Feb 2024 11:38:29 -0800
> "Paul E. McKenney" <paul...@kernel.org> wrote:
>
> > 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.
> >
> > Only build tested.
> >
> > Signed-off-by: Paul E. McKenney <paul...@kernel.org>
> > Cc: Steven Rostedt <rost...@goodmis.org>
> > Cc: Masami Hiramatsu <mhira...@kernel.org>
> > Cc: Mark Rutland <mark.rutl...@arm.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> > Cc: Ankur Arora <ankur.a.ar...@oracle.com>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > Cc: <linux-trace-ker...@vger.kernel.org>
> >
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 2da4eaa2777d6..c9e6c69cf3446 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -3156,7 +3156,7 @@ 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))
> > + if (IS_ENABLED(CONFIG_TASKS_RCU))
> > synchronize_rcu_tasks();
>
> What happens if CONFIG_TASKS_RCU is not enabled? Does
> synchronize_rcu_tasks() do anything? Or is it just a synchronize_rcu()?
It is just a synchronize_rcu().
> If that's the case, perhaps just remove the if statement and make it:
>
> synchronize_rcu_tasks();
>
> Not sure an extra synchronize_rcu() will hurt (especially after doing a
> synchronize_rcu_tasks_rude() just before hand!
That would work for me. If there are no objections, I will make this
change.
Thanx, Paul
