On Tue, 16 Oct 2018, Juri Lelli wrote:
> On 16/10/18 16:03, Peter Zijlstra wrote:
> > On Tue, Oct 16, 2018 at 03:24:06PM +0200, Thomas Gleixner wrote:
> > > It does reproduce here but with a kworker stall. Looking at the
> > > reproducer:
> > >
> > > *(uint32_t*)0x20000000 = 0;
> > > *(uint32_t*)0x20000004 = 6;
> > > *(uint64_t*)0x20000008 = 0;
> > > *(uint32_t*)0x20000010 = 0;
> > > *(uint32_t*)0x20000014 = 0;
> > > *(uint64_t*)0x20000018 = 0x9917;
> > > *(uint64_t*)0x20000020 = 0xffff;
> > > *(uint64_t*)0x20000028 = 0;
> > > syscall(__NR_sched_setattr, 0, 0x20000000, 0);
> > >
> > > which means:
> > >
> > > struct sched_attr {
> > > .size = 0,
> > > .policy = 6,
> > > .flags = 0,
> > > .nice = 0,
> > > .priority = 0,
> > > .deadline = 0x9917,
> > > .runtime = 0xffff,
> > > .period = 0,
> > > }
> > >
> > > policy 6 is SCHED_DEADLINE
> > >
> > > That makes the thread hog the CPU and prevents all kind of stuff to run.
> > >
> > > Peter, is that expected behaviour?
> >
> > Sorta, just like FIFO-99 while(1);. Except we should be rejecting the
> > above configuration, because of the rule:
> >
> > runtime <= deadline <= period
> >
> > Juri, where were we supposed to check that?
>
> Not if period == 0.
>
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2632
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2515
>
> Now, maybe we should be checking also against the default 95% cap?
If the cap is active, then yes. But you want to use the actual
configuration not the default.
Thanks,
tglx
