Hi Peter, This is indeed an important missing piece.
I think it would be worth having some simple checks, e.g.: - period_min <= period_max; - period_min >= (1ULL << DL_SCALE). To be even more picky, I'm wondering if it would be a good practice to fail the write operation if there are already dl-tasks in the system that violate the new constraint. I'm afraid there is no cheap way of achieving such check, so, I think we can skip this last tricky thing for now. Thanks, Alessio On Fri, Jul 26, 2019 at 04:54:10PM +0200, Peter Zijlstra wrote: > > Cc: Daniel Bristot de Oliveira <bris...@redhat.com> > Cc: Luca Abeni <luca.ab...@santannapisa.it> > Cc: Juri Lelli <juri.le...@redhat.com> > Cc: Dmitry Vyukov <dvyu...@google.com> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> > --- > include/linux/sched/sysctl.h | 3 +++ > kernel/sched/deadline.c | 23 +++++++++++++++++++++-- > kernel/sysctl.c | 14 ++++++++++++++ > 3 files changed, 38 insertions(+), 2 deletions(-) > > --- a/include/linux/sched/sysctl.h > +++ b/include/linux/sched/sysctl.h > @@ -56,6 +56,9 @@ int sched_proc_update_handler(struct ctl > extern unsigned int sysctl_sched_rt_period; > extern int sysctl_sched_rt_runtime; > > +extern unsigned int sysctl_sched_dl_period_max; > +extern unsigned int sysctl_sched_dl_period_min; > + > #ifdef CONFIG_UCLAMP_TASK > extern unsigned int sysctl_sched_uclamp_util_min; > extern unsigned int sysctl_sched_uclamp_util_max; > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -2597,6 +2597,14 @@ void __getparam_dl(struct task_struct *p > } > > /* > + * Default limits for DL period; on the top end we guard against small util > + * tasks still getting rediculous long effective runtimes, on the bottom end > we > + * guard against timer DoS. > + */ > +unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */ > +unsigned int sysctl_sched_dl_period_min = 100; /* 100 us */ > + > +/* > * This function validates the new parameters of a -deadline task. > * We ask for the deadline not being zero, and greater or equal > * than the runtime, as well as the period of being zero or > @@ -2608,6 +2616,8 @@ void __getparam_dl(struct task_struct *p > */ > bool __checkparam_dl(const struct sched_attr *attr) > { > + u64 period, max, min; > + > /* special dl tasks don't actually use any parameter */ > if (attr->sched_flags & SCHED_FLAG_SUGOV) > return true; > @@ -2631,12 +2641,21 @@ bool __checkparam_dl(const struct sched_ > attr->sched_period & (1ULL << 63)) > return false; > > + period = attr->sched_period; > + if (!period) > + period = attr->sched_deadline; > + > /* runtime <= deadline <= period (if period != 0) */ > - if ((attr->sched_period != 0 && > - attr->sched_period < attr->sched_deadline) || > + if (period < attr->sched_deadline || > attr->sched_deadline < attr->sched_runtime) > return false; > > + max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC; > + min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC; > + > + if (period < min || period > max) > + return false; > + > return true; > } > > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -443,6 +443,20 @@ static struct ctl_table kern_table[] = { > .proc_handler = sched_rt_handler, > }, > { > + .procname = "sched_deadline_period_max_us", > + .data = &sysctl_sched_dl_period_max, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > + { > + .procname = "sched_deadline_period_min_us", > + .data = &sysctl_sched_dl_period_min, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > + { > .procname = "sched_rr_timeslice_ms", > .data = &sysctl_sched_rr_timeslice, > .maxlen = sizeof(int), > >