linux-kernel - Re: [RFC][PATCH 12/13] sched/deadline: Introduce deadline servers

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Date:   Thu, 8 Aug 2019 09:56:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     mingo@...nel.org, juri.lelli@...hat.com,
        linux-kernel@...r.kernel.org, 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 12/13] sched/deadline: Introduce deadline servers

On Wed, Aug 07, 2019 at 06:31:59PM +0200, Dietmar Eggemann wrote:
> On 7/26/19 4:54 PM, Peter Zijlstra wrote:
> > 
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> [...]
> 
> > @@ -889,6 +891,8 @@ static void update_curr(struct cfs_rq *c
> >  		trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
> >  		cgroup_account_cputime(curtask, delta_exec);
> >  		account_group_exec_runtime(curtask, delta_exec);
> > +		if (curtask->server)
> > +			dl_server_update(curtask->server, delta_exec);
> >  	}
> 
> I get a lockdep_assert_held(&rq->lock) related warning in start_dl_timer()
> when running the full stack.

That would seem to imply a stale curtask->server value; the hunk below:

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3756,8 +3756,11 @@ pick_next_task(struct rq *rq, struct tas

        for_each_class(class) {
                p = class->pick_next_task(rq, NULL, NULL);
-               if (p)
+               if (p) {
+                       if (p->sched_class == class && p->server)
+                               p->server = NULL;
                        return p;
+               }
        }


Was supposed to clear p->server, but clearly something is going 'funny'.