linux-kernel - Re: [PATCH 1/1] psi: do not require setsched permission from the trigger creator

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Message-ID: <20190730081122.GH31381@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Jul 2019 10:11:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     mingo@...hat.com, lizefan@...wei.com, hannes@...xchg.org,
        axboe@...nel.dk, dennis@...nel.org, dennisszhou@...il.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, Nick Kralevich <nnk@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/1] psi: do not require setsched permission from the
 trigger creator

On Mon, Jul 29, 2019 at 06:33:10PM -0700, Suren Baghdasaryan wrote:
> When a process creates a new trigger by writing into /proc/pressure/*
> files, permissions to write such a file should be used to determine whether
> the process is allowed to do so or not. Current implementation would also
> require such a process to have setsched capability. Setting of psi trigger
> thread's scheduling policy is an implementation detail and should not be
> exposed to the user level. Remove the permission check by using _nocheck
> version of the function.
> 
> Suggested-by: Nick Kralevich <nnk@...gle.com>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  kernel/sched/psi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 7acc632c3b82..ed9a1d573cb1 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1061,7 +1061,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
>  			mutex_unlock(&group->trigger_lock);
>  			return ERR_CAST(kworker);
>  		}
> -		sched_setscheduler(kworker->task, SCHED_FIFO, &param);
> +		sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, &param);

ARGGH, wtf is there a FIFO-99!! thread here at all !?

>  		kthread_init_delayed_work(&group->poll_work,
>  				psi_poll_work);
>  		rcu_assign_pointer(group->poll_kworker, kworker);
> -- 
> 2.22.0.709.g102302147b-goog
>