linux-kernel - Re: [PATCH v2, RESEND] sched/rt: Try to restart rt period timer when rt runtime exceeded

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Message-ID: <YanElPGuGJ8J6UK9@kroah.com>
Date:   Fri, 3 Dec 2021 08:17:40 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Li Hua <hucool.lihua@...wei.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2, RESEND] sched/rt: Try to restart rt period timer when
 rt runtime exceeded

On Fri, Dec 03, 2021 at 03:36:18AM +0000, Li Hua wrote:
> When rt_runtime is modified from -1 to a valid control value, it may
> cause the task to be throttled all the time. Operations like the following
> will trigger the bug. E.g:
> 1. echo -1 > /proc/sys/kernel/sched_rt_runtime_us
> 2. Run a FIFO task named A that executes while(1)
> 3. echo 950000 > /proc/sys/kernel/sched_rt_runtime_us
> 
> When rt_runtime is -1, The rt period timer will not be activated when task
> A enqueued. And then the task will be throttled after setting rt_runtime to
> 950,000. The task will always be throttled because the rt period timer is
> not activated.
> 
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Li Hua <hucool.lihua@...wei.com>
> ---
> v1->v2:
>   - call do_start_rt_bandwidth to reduce repetitive code.
>   - use raw_spin_lock_irqsave to avoid deadlock on a timer context.
> ---
>  kernel/sched/rt.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>