On Thu, Jul 02, 2026 at 06:11:25PM +0800, Zqiang wrote:
> In the rcu_nocb_toggle(), the schedule_hrtimeout() is called after the
> state assignment with no condition check. the release-acquire pair from
> raw_spin_unlock/lock(&cpu_base->lock), guarantee that task->__state is
> visible to the hrtimer callback:
>
> CPU0 CPU1
> __set_current_state(TASK_INTERRUPTIBLE)
> ->WRITE_ONCE(task->__state, TASK_INTERRUPTIBLE)
> schedule_hrtimeout
> ->hrtimer_sleeper_start_expires()
> ->raw_spin_lock_irqsave(&cpu_base->lock)
> ....
> ->raw_spin_unlock_irqrestore(&cpu_base->lock)
>
> hard-irq:
>
> raw_spin_lock_irqsave(&cpu_base->lock)
> __hrtimer_run_queues
> ->__run_hrtimer
>
> ->raw_spin_unlock_irqrestore(&cpu_base->lock)
> ->fn(timer)
> ->hrtimer_wakeup
> ->wake_up_process
> ->try_to_wake_up
> ->READ
> task->__state
>
> This commit therefore use the __set_current_state() to replace the
> set_current_state() in rcu_nocb_toggle().
>
> Signed-off-by: Zqiang <[email protected]>
This looks correct, and either drops an smp_mb() or converts an
xchg() to a WRITE_ONCE(), which does decrease overhead. Except that
rcu_nocb_toggle() is invoked very infrequently and has high overhead
that I would expect to lose this overhead decrease in the noise. And it
forces those reading the code to go figure out what is different between
set_current_state() and __set_current_state().
So I am not convinced to take this patch. But am I missing something here?
Thanx, Paul
> ---
> kernel/rcu/rcutorture.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index b1bab59efde5..a0e6901e0f90 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -2947,7 +2947,7 @@ static int rcu_nocb_toggle(void *arg)
> atomic_long_inc(&n_nocb_deoffload);
> }
> toggle_delay = torture_random(&rand) % toggle_fuzz +
> toggle_interval;
> - set_current_state(TASK_INTERRUPTIBLE);
> + __set_current_state(TASK_INTERRUPTIBLE);
> schedule_hrtimeout(&toggle_delay, HRTIMER_MODE_REL);
> if (stutter_wait("rcu_nocb_toggle"))
> sched_set_normal(current, oldnice);
> --
> 2.17.1
>
