linux-kernel - Re: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190729111510.GD31398@hirez.programming.kicks-ass.net>
Date:   Mon, 29 Jul 2019 13:15:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        dietmar.eggemann@....com, luca.abeni@...tannapisa.it,
        bristot@...hat.com, balsini@...roid.com, dvyukov@...gle.com,
        tglx@...utronix.de, vpillai@...italocean.com, rostedt@...dmis.org
Subject: Re: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs
 pick_next_task

On Mon, Jul 29, 2019 at 11:25:19AM +0200, Juri Lelli wrote:
> Hi,
> 
> On 26/07/19 16:54, Peter Zijlstra wrote:
> > Because pick_next_task() implies set_curr_task() and some of the
> > details haven't matter too much, some of what _should_ be in
> > set_curr_task() ended up in pick_next_task, correct this.
> > 
> > This prepares the way for a pick_next_task() variant that does not
> > affect the current state; allowing remote picking.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> >  kernel/sched/deadline.c |   23 ++++++++++++-----------
> >  kernel/sched/rt.c       |   27 ++++++++++++++-------------
> >  2 files changed, 26 insertions(+), 24 deletions(-)
> > 
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -1694,12 +1694,21 @@ static void start_hrtick_dl(struct rq *r
> >  }
> >  #endif
> >  
> > -static inline void set_next_task(struct rq *rq, struct task_struct *p)
> > +static void set_next_task_dl(struct rq *rq, struct task_struct *p)
> >  {
> >  	p->se.exec_start = rq_clock_task(rq);
> >  
> >  	/* You can't push away the running task */
> >  	dequeue_pushable_dl_task(rq, p);
> > +
> > +	if (hrtick_enabled(rq))
> > +		start_hrtick_dl(rq, p);
> > +
> > +	if (rq->curr->sched_class != &dl_sched_class)
> > +		update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
> > +
> > +	if (rq->curr != p)
> > +		deadline_queue_push_tasks(rq);
> 
> It's a minor thing, but I was wondering why you added the check on curr.
> deadline_queue_push_tasks() already checks if are there pushable tasks,
> plus curr can still be of a different class at this point?

Hmm, so by moving that code into set_next_task() it is exposed to the:

  if (queued)
    deuque_task();
  if (running)
    put_prev_task();

  /* do stuff */

  if (queued)
    enqueue_task();
  if (running)
    set_next_task();

patter from core.c; and in that case nothing changes. That said; I
might've gotten it wrong.