Re: [PATCH RFC -rcu/dev] hazptrtorture: Release all deferred hazard pointers before stopping

[Andrea Parri <parri.andrea@gmail.com>]

On Thu, Oct 22, 2026 at 03:55:44PM -0700, Paul E. McKenney wrote:
> On Thu, Oct 22, 2026 at 02:55:55PM +0200, Andrea Parri wrote:

[...]

> Then let's please keep the torture_must_stop() check.  Yes, there is
> still a window between the return from torture_must_stop() and the
> call to torture_hrtimeout_ms(), but maybe that is something to take
> care of later on.

Will do.

[...]

> Yes, agreed, almost:
>
> o	Keep the hazptr_torture_do_pending() do-while loop as it
> 	is, but add the for_each_possible_cpu() after loop exit.
>
> o	Stop the readers first, stop hazptr_torture_do_pending()
> 	to flush out anything left from the readers, then stop
> 	the writer.
>
> However, for the "almost", note that the "while (!torture_must_stop())"
> needs to become "while (!kthread_should_stop())".  If this change is
> not made, then hazptr_torture_do_pending() will exit its do-while loop
> as soon as hazptr_torture_cleanup() calls torture_cleanup_begin().
> This will of course defeat the reordering.
>
> Does that work, or am I still missing something?

do_pending does leave the loop then, but the final pass goes after
torture_kthread_stopping(), not right after the loop:

	} while (!torture_must_stop());
	torture_kthread_stopping("hazptr_torture_do_pending");
	/* The readers have stopped, so nothing new can be deferred. */
	for_each_possible_cpu(cpu)
		hazptr_torture_do_one_pending(cpu, &rand);
	return 0;

torture_kthread_stopping() sleeps HZ/20 at a time until
kthread_should_stop(), so the pass runs only once
hazptr_torture_cleanup() stops do_pending, after the readers.

With "while (!kthread_should_stop())" and the torture_must_stop()
check before the sleep, do_pending would instead spin without sleeping
from torture_cleanup_begin() until it is stopped.

> Alternatively, you could keep the current do-while condition and place
> a loop around your post-do-while code like this:
>
> 	while (!kthread_should_stop())
> 		for_each_possible_cpu(cpu)
> 			hazptr_torture_do_one_pending(cpu, &rand);
>
> But changing the do-while condition looks cleaner to me.

That loop would spin too.

> This code will also need adjustment when something like a call_hazptr()
> is added, presumably along with a hazptr_barrier(), but we can worry
> about that when it happens.

Agreed.

I have been running this version locally, with the rest of v1: a
30-minute PREEMPT run, and a 30-minute NOPREEMPT run with
torture_type=hazptr, pass.  With kthread_do_pending_ms=10000, the
shutdown still takes less than 150ms.  If it works for you, v1 will
have it.

Thanks,
  Andrea