Messages in this thread Patch in this message | | | Date | Mon, 14 Mar 2022 16:00:44 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH] genirq/msi: Shutdown managed interrupts with unsatifiable affinities |
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On Mon, 14 Mar 2022 15:27:10 +0000, Thomas Gleixner <tglx@linutronix.de> wrote: > > On Mon, Mar 07 2022 at 19:06, Marc Zyngier wrote: > > When booting with maxcpus=<small number>, interrupt controllers > > such as the GICv3 ITS may not be able to satisfy the affinity of > > some managed interrupts, as some of the HW resources are simply > > not available. > > This is also true if you have offlined lots of CPUs, right?
Not quite. If you offline the CPUs, the interrupts will be placed in the shutdown state as expected, having initially transitioned via an activation state with an online CPU. The issue here is with the initial activation of the interrupt, which currently happens even if no matching CPU is present.
> > > In order to deal with this, do not try to activate such interrupt > > if there is no online CPU capable of handling it. Instead, place > > it in shutdown state. Once a capable CPU shows up, it will be > > activated. > > > > Reported-by: John Garry <john.garry@huawei.com> > > Reported-by: David Decotigny <ddecotig@google.com> > > Signed-off-by: Marc Zyngier <maz@kernel.org> > > --- > > kernel/irq/msi.c | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > > > > diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c > > index 2bdfce5edafd..aa84ce84c2ec 100644 > > --- a/kernel/irq/msi.c > > +++ b/kernel/irq/msi.c > > @@ -818,6 +818,18 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag > > irqd_clr_can_reserve(irqd); > > if (vflags & VIRQ_NOMASK_QUIRK) > > irqd_set_msi_nomask_quirk(irqd); > > + > > + /* > > + * If the interrupt is managed but no CPU is available > > + * to service it, shut it down until better times. > > + */ > > + if ((vflags & VIRQ_ACTIVATE) && > > + irqd_affinity_is_managed(irqd) && > > + !cpumask_intersects(irq_data_get_affinity_mask(irqd), > > + cpu_online_mask)) { > > + irqd_set_managed_shutdown(irqd); > > Hrm. Why is this in the !CAN_RESERVE path and not before the actual > activation call?
VIRQ_CAN_RESERVE can only happen as a consequence of GENERIC_IRQ_RESERVATION_MODE, which only exists on x86. Given that x86 is already super careful not to activate an interrupt that is not immediately required, I though we could avoid putting this check on that path.
But if I got the above wrong (which is, let's face it, extremely likely), I'm happy to kick it down the road next to the activation call.
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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