linux-kernel - Re: [patch 2/2] tick/broadcast: Handle spurious interrupts gracefully

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Date:	Mon, 6 Jul 2015 17:36:21 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sudeep Holla <sudeep.holla@....com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Andriy Gapon <avg@...ebsd.org>
Subject: Re: [patch 2/2] tick/broadcast: Handle spurious interrupts
 gracefully

On Mon, 6 Jul 2015, Sudeep Holla wrote:
> On Sun, Jul 5, 2015 at 9:53 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > Andriy reported that on a virtual machine the warning about negative
> > expiry time in the clock events programming code triggered:
> >
> > hpet: hpet0 irq 40 for MSI
> > hpet: hpet1 irq 41 for MSI
> > Switching to clocksource hpet
> > WARNING: at kernel/time/clockevents.c:239
> >
> > [<ffffffff810ce6eb>] clockevents_program_event+0xdb/0xf0
> > [<ffffffff810cf211>] tick_handle_periodic_broadcast+0x41/0x50
> > [<ffffffff81016525>] timer_interrupt+0x15/0x20
> >
> > When the second hpet is installed as a per cpu timer the broadcast
> > event is not longer required and stopped, which sets the next_evt of
> > the broadcast device to KTIME_MAX.
> >
> > If after that a spurious interrupt happens on the broadcast device,
> > then the current code blindly handles it and tries to reprogram the
> > broadcast device afterwards, which adds the period to
> > next_evt. KTIME_MAX + period results in a negative expiry value
> > causing the WARN_ON in the clockevents code to trigger.
> >
> > Add a proper check for the state of the broadcast device into the
> > interrupt handler and return if the interrupt is spurious.
> >
> > Reported-by: Andriy Gapon <avg@...eBSD.org>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  kernel/time/tick-broadcast.c |    7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > Index: tip/kernel/time/tick-broadcast.c
> > ===================================================================
> > --- tip.orig/kernel/time/tick-broadcast.c
> > +++ tip/kernel/time/tick-broadcast.c
> > @@ -301,6 +301,13 @@ static void tick_handle_periodic_broadca
> >         bool bc_local;
> >
> >         raw_spin_lock(&tick_broadcast_lock);
> > +
> > +       /* Handle spurious interrupts gracefully */
> > +       if (clockevent_state_shutdown(&tick_broadcast_device.evtdev)) {
> 
> I tried this patch along with 1/2, found that this generating warning as
> tick_broadcast_device.evtdev is of type ‘struct clock_event_device *’ already,
> so it can be passed directly.

Right you are. The heat is melting my brain ...