linux-kernel - Re: [PATCH v7 1/2] sched/rt: fix bad task migration for rt tasks

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Message-ID: <43de1f15-42cf-45ea-db5c-30de976a6828@arm.com>
Date:   Fri, 26 Aug 2022 20:45:54 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Schspa Shi <schspa@...il.com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org, zhaohui.shi@...izon.ai
Subject: Re: [PATCH v7 1/2] sched/rt: fix bad task migration for rt tasks

On 13/07/2022 15:48, Schspa Shi wrote:
> Commit 95158a89dd50 ("sched,rt: Use the full cpumask for balancing")
> allow find_lock_lowest_rq to pick a task with migration disabled.
> This commit is intended to push the current running task on this CPU
> away.
> 
> There is a race scenario, which allows a migration disabled task to
> be migrated to another CPU.
> 
> When there is a RT task with higher priority, rt sched class was
> intended to migrate higher priority task to lowest rq via push_rt_tasks,
> this BUG will happen here.
       ^^^

You mean the warning in set_task_cpu()?

> With the system running on PREEMPT_RT, rt_spin_lock will disable
> migration, this will make the problem easier to reproduce.
> 
> I have seen this crash on PREEMPT_RT, from the logs, there is a race
                   ^^^^^
                     ?

We still talking about the set_task_cpu() warning, right?

[...]

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>

You should carry the Reviewed-by:'s you got in previous versions.