On Sat, Sep 05, 2026 at 10:08:30PM +0100, Bradley Morgan wrote:
> On 5 September 2026 21:40:28 BST, "Paul E. McKenney" <[email protected]>
> wrote:
> >On Fri, Sep 04, 2026 at 06:28:45PM +0100, Bradley Morgan wrote:
> >> On 4 September 2026 17:00:22 BST, "Paul E. McKenney"
> ><[email protected]>
> >> wrote:
> >> >On Fri, Sep 04, 2026 at 09:01:05AM -0400, Mathieu Desnoyers wrote:
> >> >> On 2026-08-03 20:03, Bradley Morgan wrote:
> >> >> > The do_pending kthread never sleeps. Its supposed to.
> >> >> > kthread_do_pending_ms sets the gap between cleanups, and the docs
> >> >> > say so too. But the sleep sits behind torture_must_stop(), and
> >thats
> >> >> > false while the test runs. So the kthread never sleeps. It just
> >loops.
> >> >> > It drains the pending lists over and over, no pause, and burns a
> >full
> >> >> > CPU for the whole test.
> >> >>
> >> >> Paul, I just found this patch in my junk email folder. Maybe relevant
> >> >> for you ?
> >> >
> >> >We got it in my -rcu tree:
> >> >
> >> >15b9fca2f5ce ("hazptrtorture: Fix inverted sleep condition in
> >do_pending
> >> >kthread")
> >> >
> >> >But I do appreciate your checking for missed patches, thank you!
> >> >
> >> > Thanx, Paul
> >> >
> >> >> Thanks,
> >> >>
> >> >> Mathieu
> >> >>
> >> >> >
> >> >> > Flip the check. With !torture_must_stop() it sleeps for
> >> >> > kthread_do_pending_ms between passes. When the test stops it does
> >one
> >> >> > last cleanup and exits. Nothing left to do, so no sleep needed
> >then.
> >> >> >
> >> >> > Fixes: 94d2e93c222e ("hazptrtorture: Add kthread to release
> >deferred
> >> >hazard pointers")
> >> >> > Signed-off-by: Bradley Morgan <[email protected]>
> >> >> > ---
> >> >> > kernel/rcu/hazptrtorture.c | 2 +-
> >> >> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >> >> >
> >> >> > diff --git a/kernel/rcu/hazptrtorture.c
> >b/kernel/rcu/hazptrtorture.c
> >> >> > index 72aeb50668e9..7c8b5899fb01 100644
> >> >> > --- a/kernel/rcu/hazptrtorture.c
> >> >> > +++ b/kernel/rcu/hazptrtorture.c
> >> >> > @@ -555,7 +555,7 @@ static int hazptr_torture_do_pending(void *arg)
> >> >> > cpu = cpumask_next_wrap(cpu, cpu_possible_mask);
> >> >> > hazptr_torture_do_one_pending(cpu, &rand);
> >> >> > }
> >> >> > - if (torture_must_stop())
> >> >> > + if (!torture_must_stop())
> >> >> > torture_hrtimeout_ms(kthread_do_pending_ms,
> >> >> > USEC_PER_MSEC, &rand);
> >> >> > // Omit stutter_wait() because this function needs to
> >> >> > do cleanup.
> >> >> > } while (!torture_must_stop());
> >> >>
> >> >>
> >> >> --
> >> >> Mathieu Desnoyers
> >> >> EfficiOS Inc.
> >> >> https://www.efficios.com
> >> >
> >> >
> >> Hi, new email.
> >>
> >> Could I ask where the heck hazptr is? Its not in next, would you like,
> >> help???
> >>
> >> --- Thanks!
> >>
> >https://lore.kernel.org/all/[email protected]/
> >
> >It is still in my -rcu tree.
> >
> >I would not say "no" to a fix for this issue:
> >
> >https://lore.kernel.org/all/[email protected]/
> >
> >Once that is in place, I would be happy to put this back into -next.
> >
> >At some point, we will need to get rid of the concept of wildcard hazard
> >pointers, as those end up instead emulating RCU, but I don't see that
> >as an immediate obstacle.
>
> Well, okay, tell me more and I'll develop it.
I must confess that I have not looked much into that bug report, so I
don't have much more to tell.
Thanx, Paul
> --- Thanks!
> https://lore.kernel.org/all/[email protected]/
>
