linux-kernel - Re: [v6.12] WARNING: at kernel/sched/deadline.c:1995 enqueue_dl_entity (task blocked for more than 28262 seconds)

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Message-ID: <CAO7JXPjckPaW7=dkCGUk-yD+CgNW9iN4TpkknCeTkmBAZ2u1OQ@mail.gmail.com>
Date: Mon, 9 Dec 2024 09:12:25 -0500
From: Vineeth Remanan Pillai <vineeth@...byteword.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Joel Fernandes <joel@...lfernandes.org>, Ilya Maximets <i.maximets@....org>, 
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, vineethrp@...gle.com, 
	shraash@...gle.com, marcel.ziswiler@...ethink.co.uk
Subject: Re: [v6.12] WARNING: at kernel/sched/deadline.c:1995
 enqueue_dl_entity (task blocked for more than 28262 seconds)

> > >
> > > Which then also goes *bang*. The above can't happen if we clear
> > > current->dl_server in dl_stop_server().
> > >
> > I also thought this could be a possibility but the previous deactivate
> > for this task would have cleared the dl_server no?
>
> That gets cleared in put_prev_set_next_task(), which gets called *after*
> pick_next_task() completes. So until that time, current will have
> dl_server set.
>
Ahh ok that makes sense.

> > Soon after this in
> > update_curr() we again call dl_server_update if p_.dl_server !=
> > rq->fair_server and this is also another possibility of a double
> > enqueue.
>
> Right, there's few possible paths there, I've not fully mapped them. But
> I think clearing ->dl_server in dl_server_stop() is the cleanest option
> for this.
>
Even clearing would not help here as it will still make this condition
true (NULL != &rq->fair_server). Now that we have the dl_active flag,
we should probably check dl_se->dl_active before doing the
dl_server_update.

Thanks,
Vineeth