Re: [PATCH] hazptrtorture: Fix inverted sleep condition in do_pending kthread

[Bradley Morgan <brads@mainlining.org>]

On 5 September 2026 23:54:38 BST, "Paul E. McKenney" <paulmck@kernel.org>
wrote:
>On Sat, Sep 05, 2026 at 10:08:30PM +0100, Bradley Morgan wrote:
>> On 5 September 2026 21:40:28 BST, "Paul E. McKenney"
><paulmck@kernel.org>
>> 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"
>> ><paulmck@kernel.org>
>> >> 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 <include@grrlz.net>
>> >> >> > ---
>> >> >> >   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/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
>> >
>> >It is still in my -rcu tree.
>> >
>> >I would not say "no" to a fix for this issue:
>> >
>>
>>https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
>> >
>> >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.

No, like the getting rid of wildcard hazptrs?

>
>						Thanx, Paul
>
>> --- Thanks!
>>
>https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/
>> 

--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/