From: Oleg Nesterov <oleg@redhat.com>
To: cheng chao <chengchao@kedacom.com>
Cc: mingo@kernel.org, peterz@infradead.org, tj@kernel.org,
akpm@linux-foundation.org, chris@chris-wilson.co.uk,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/core: simpler function for sched_exec migration
Date: Mon, 5 Sep 2016 15:11:48 +0200 [thread overview]
Message-ID: <20160905131147.GA8552@redhat.com> (raw)
In-Reply-To: <1473056403-7877-1-git-send-email-chengchao@kedacom.com>
On 09/05, cheng chao wrote:
>
> @@ -2958,7 +2958,7 @@ void sched_exec(void)
> struct migration_arg arg = { p, dest_cpu };
>
> raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> - stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
> + stop_one_cpu_sync(task_cpu(p), migration_cpu_stop, &arg);
> return;
> }
> unlock:
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index 4a1ca5f..24f8637 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -130,6 +130,27 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
> return done.ret;
> }
>
> +/**
> + * the caller keeps task_on_rq_queued, so it's more suitable for
> + * sched_exec on the case when needs migration
> + */
> +void stop_one_cpu_sync(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
> +{
> + struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = NULL };
> +
> + if (!cpu_stop_queue_work(cpu, &work))
> + return;
> +
> +#if defined(CONFIG_PREEMPT_NONE) || defined(CONFIG_PREEMPT_VOLUNTARY)
> + /*
> + * CONFIG_PREEMPT doesn't need call schedule here, because
> + * preempt_enable already does the similar thing when call
> + * cpu_stop_queue_work
> + */
> + schedule();
> +#endif
> +}
Honestly, I don't really understand the changelog, but this looks wrong.
stop_one_cpu_sync() assumes that cpu == smp_processor_id/task_cpu(current),
and thus the stopper thread should preempt us at least after schedule()
(if CONFIG_PREEMPT_NONE), so we do not need to synchronize.
But this is not necessarily true? This task can migrate to another CPU
before cpu_stop_queue_work() ?
Oleg.
next prev parent reply other threads:[~2016-09-05 13:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-05 6:20 [PATCH] sched/core: simpler function for sched_exec migration cheng chao
2016-09-05 13:11 ` Oleg Nesterov [this message]
2016-09-06 2:11 ` chengchao
2016-09-06 15:22 ` Oleg Nesterov
2016-09-07 3:22 ` chengchao
2016-09-07 12:35 ` Oleg Nesterov
2016-09-08 2:17 ` chengchao
2016-09-09 10:05 ` Peter Zijlstra
2016-09-09 1:39 ` [lkp] [sched/core] 3d26b7622f: BUG: unable to handle kernel NULL pointer dereference at 00000001 kernel test robot
2016-09-09 2:04 ` chengchao
2016-09-09 2:26 ` Ye Xiaolong
2016-09-09 2:36 ` chengchao
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