sched/psi: Do not require setsched permission from the trigger creator

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: lizefan@huawei.com
Cc: mingo@redhat.com
Cc: akpm@linux-foundation.org
Cc: kernel-team@android.com
Cc: dennisszhou@gmail.com
Cc: dennis@kernel.org
Cc: hannes@cmpxchg.org
Cc: axboe@kernel.dk
Link: https://lkml.kernel.org/r/20190730013310.162367-1-surenb@google.com

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7fe2c5fd26b54f42082727957c5066bab7207b3d..23fbbcc414d5d739507ac1f8ecb5757c87a9ce55 100644 (file)
--- 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);
                kthread_init_delayed_work(&group->poll_work,
                                psi_poll_work);
                rcu_assign_pointer(group->poll_kworker, kworker);