linux-kernel - Re: [PATCH v4 1/2] sched/rt: fix bad task migration for rt tasks

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Message-ID: <20220711161037.06b8c1ea@gandalf.local.home>
Date:   Mon, 11 Jul 2022 16:10:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] sched/rt: fix bad task migration for rt tasks

On Sat, 09 Jul 2022 05:32:25 +0800
Schspa Shi <schspa@...il.com> wrote:

> >> +++ b/kernel/sched/rt.c
> >> @@ -1998,11 +1998,14 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
> >>  			 * the mean time, task could have
> >>  			 * migrated already or had its affinity changed.
> >>  			 * Also make sure that it wasn't scheduled on its rq.
> >> +			 * It is possible the task has running for a while,  
> >
> > I don't understand the "running for a while" part. That doesn't make sense.
> >  
> 
> When I say "run for a while" I mean as long as the task has
> run capability, we should check the migrate disabled flag again.
> 
> > The only way this can happen is that it was scheduled, set
> > "migrate_disabled" and then got preempted where it's no longer on the run
> > queue.  
> 
> Yes, it is the only case.

Can we then change the comment, as the "running for a while" is not clear
to what the issue is, and honestly, sounds misleading.

-- Steve