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

[Peter Zijlstra <peterz@infradead.org>]

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@google.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.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
>