Re: [RESEND PATCH v4] sched: do not call __put_task_struct() on rt if pi_blocked_on is set

[Sebastian Andrzej Siewior]

On 2025-06-17 11:26:09 [+0200], Peter Zijlstra wrote:
> On Fri, Jun 13, 2025 at 12:05:14PM -0300, Luis Claudio R. Goncalves wrote:
> > With PREEMPT_RT enabled, some of the calls to put_task_struct() coming
> > from rt_mutex_adjust_prio_chain() could happen in preemptible context and
> > with a mutex enqueued. That could lead to this sequence:
> > 
> >         rt_mutex_adjust_prio_chain()
> >           put_task_struct()
> >             __put_task_struct()
> >               sched_ext_free()
> >                 spin_lock_irqsave()
> >                   rtlock_lock() --->  TRIGGERS
> >                                       lockdep_assert(!current->pi_blocked_on);
> > 
> > Fix that by unconditionally resorting to the deferred call to
> > __put_task_struct() if PREEMPT_RT is enabled.
> > 
> 
> Should this have a Fixes: tag and go into /urgent?

I would say so. I'm not sure what caused it. I think Luis said at some
point that it is caused by a sched_ext case or I mixed it up with
something. Luis?

The other question I have, do we need to distinguish between PREEMPT_RT
and not or can we do this unconditionally?

Sebastian