Re: [PATCH 1/6] sched/proxy: Remove superfluous clear_task_blocked_in()

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Peter,

On 5/29/2026 2:17 PM, Peter Zijlstra wrote:
> Egads, this is terrible. This means all is_blocked tasks always end up
> taking blocked_lock.
> 
> The other suggestion (in the other subthread) was to simply delay this
> patch until the end. That seems far more sensible.
>
> Anyway, let me go try and find your git tree and see what you ended up> with.

Now that I look at this again, yeah, you can simply move that
optimization later too. Github isn't letting me push the branch but
essentially you move:

  e2ff8b7bde07 sched/proxy: Only return migrate when needed
  1b89b7b21bf5 sched/proxy: Remove superfluous clear_task_blocked_in()

to happen after commit a8be1edac5a1 ("sched/proxy: Remove
PROXY_WAKING").

All of that was for essentially this scenario:

mutex_lock()
  set_task_blocked_on(mutex)
  schedule_preempt_disabled()
    __schedule()
      p->is_blocked = 1
      
      -------> preempted                  __send_signal_locked()
                                            signal_wake_up()
                                              try_to_wake_up()
                                                ttwu_runnable()
                                                  /*
                                                   * Needs to clear p->blocked_on
                                                   * As long as PROXY_WAKING exists.
                                                   */
                                                   ttwu_do_wakeup()
                                                     p->__state = TASK_RUNNING
                                                     p->is_blocked = 0

                                          mutex_unlock()
                                            set_task_blocked_on_waking(p, mutex)
                                               p->blocked_on = PROXY_WAKING;

      /* p->is_blocked = 0; p->blocked_on = PROXY_WAKING */
      
      next = p;
    <------ swich_in

  /* Exits out of schedule_preempt_disabled() */
  set_task_blocked_on(p, mutex)

  !!! p->blocked_on == PROXY_WAKING !!!

-- 
Thanks and Regards,
Prateek