Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

From: Rafael J. Wysocki
Date: Tue Apr 28 2015 - 08:19:18 EST

On Tue, Apr 28, 2015 at 12:42 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> On 28/04/15 11:34, Daniel Lezcano wrote:
>> On 04/28/2015 12:11 PM, Linus Walleij wrote:
>>> On Thu, Apr 2, 2015 at 12:22 AM, Rafael J. Wysocki
>>> <rjw@xxxxxxxxxxxxx> wrote:
>>>> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>>> Replace the clockevents_notify() call with an explicit function
>>>> call.
>>>> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>> For some reason this makes my Ux500 system arbitrarily hang,
>>> especially during boot. Bisected down to this commit. Since the
>>> entire changeset is removing the notifications altogether I can't
>>> just revert it.
>>> Disabling CONFIG_CPU_IDLE removes the problem.
>>> Tried registering a stub driver (I just #if 0 all the code in
>>> drivers/cpuidle/cpuidle-ux500.c) it still crashes.
>>> That makes me think something inside the cpuidle subsystem is
>>> locking up after this, but my other idea is that the timer may be
>>> involved in some way, like this is stressing the timer in some new
>>> yet untested way.
>>> Has anyone else seen problems with this or is it only ux500?
>>> I'm looking closer at it but feel a bit clueless...
>> If you keep the #if 0 and remove the CPUIDLE_FLAG_TIMER_STOP flag,
>> does it still crash ?
> 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

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