>
> 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?
Nothing was missed, only from memory ordering perspective,
using set_current_state() is unnecessary.
furthermore, in RCU tasks, we used the following code:
__set_current_state(TASK_IDLE); // in this we use __set_current_state()
schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD);
Or perhaps we could also add a comment something like
this(kernel/time/sleep_timeout.c):
/*
* __set_current_state() can be used in schedule_timeout_*() functions, because
* schedule_timeout() calls schedule() unconditionally.
*/
Thanks
Zqiang
>
> 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
> >
>
