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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
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Subject: Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function
Date: Tue, 28 Apr 2015 15:37:44 +0200
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On Tuesday, April 28, 2015 03:31:54 PM Rafael J. Wysocki wrote:
> On Tuesday, April 28, 2015 02:37:10 PM Linus Walleij wrote:
> > On Tue, Apr 28, 2015 at 2:19 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> > > Sudeep:
> > >> At-least I observed issue only when I am using hardware broadcast timer.
> > >> It doesn't hang when I am using hrtimer as broadcast timer in which case
> > >> one of the cpu will be not enter deeper idle states that lose timer.
> > >> I will rerun on v4.1-rc1 and post the complete log.
> > >
> > > So the bug here is that cpuidle_enter() enables interrupts, so the
> > > assumption about them being not enabled made by
> > > tick_broadcast_oneshot_control() is actually not valid.
> > >
> > > It looks like we need to acquire the clockevents_lock at least in this
> > > particular case.  Let me see where to put it and I'll send a patch for
> > > testing.
> > 
> > Aha that looks very much like it. Put me on the patch and I'll
> > take it for a spin.
> 
> OK, so something like the below for starters (the _irqsave variant is used to
> avoid adding one more WARN_ON(irqs_disabled()) in there).
> 
> I haven't tested it, but then I can't reproduce the original issue in the
> first place.

Of course, the whole "broadcast" thing could be done from cpuidle_enter()
in the first place, but then we could not avoid the problem with the cpuidle
*callback* enabling interrupts possibly in there anyway (not to mention the
"coupled" stuff).


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.