On Tue, Jul 30, 2019 at 1:11 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > 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@xxxxxxxxxx> > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > --- > > 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, ¶m); > > + sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m); > > ARGGH, wtf is there a FIFO-99!! thread here at all !? We need psi poll_kworker to be an rt-priority thread so that psi notifications are delivered to the userspace without delay even when the CPUs are very congested. Otherwise it's easy to delay psi notifications by running a simple CPU hogger executing "chrt -f 50 dd if=/dev/zero of=/dev/null". Because these notifications are time-critical for reacting to memory shortages we can't allow for such delays. Notice that this kworker is created only if userspace creates a psi trigger. So unless you are using psi triggers you will never see this kthread created. > > kthread_init_delayed_work(&group->poll_work, > > psi_poll_work); > > rcu_assign_pointer(group->poll_kworker, kworker); > > -- > > 2.22.0.709.g102302147b-goog > > > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. >
