Re: [PATCH 2/2 v5] KVM: PPC: booke: Add watchdog emulation

[Scott Wood <scottwood@freescale.com>]

On 07/21/2012 03:37 AM, Bhushan Bharat-R65777 wrote:
> 
> 
>> -----Original Message-----
>> From: Wood Scott-B07421
>> Sent: Saturday, July 21, 2012 2:59 AM
>> To: Bhushan Bharat-R65777
>> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; agraf@suse.de; Bhushan Bharat-
>> R65777
>> Subject: Re: [PATCH 2/2 v5] KVM: PPC: booke: Add watchdog emulation
>>
>> On 07/20/2012 12:00 AM, Bharat Bhushan wrote:
>>> +static void arm_next_watchdog(struct kvm_vcpu *vcpu) {
>>> +	unsigned long nr_jiffies;
>>> +
>>> +	spin_lock(&vcpu->arch.wdt_lock);
>>> +	nr_jiffies = watchdog_next_timeout(vcpu);
>>> +	/*
>>> +	 * If the number of jiffies of watchdog timer >= NEXT_TIMER_MAX_DELTA
>>> +	 * then do not run the watchdog timer as this can break timer APIs.
>>> +	 */
>>> +	if (nr_jiffies < NEXT_TIMER_MAX_DELTA)
>>> +		mod_timer(&vcpu->arch.wdt_timer, jiffies + nr_jiffies);
>>> +	else
>>> +		del_timer(&vcpu->arch.wdt_timer);
>>> +	spin_unlock(&vcpu->arch.wdt_lock);
>>> +}
>>
>> This needs to be an irqsave lock.
> 
> Ok, I want to understood why irqsave lock should be used here?
>
> irqsave_lock is used when the critical section within lock can be
> referenced from interrupt context also. What part of critical section
> above can get affected from local irq? Is it jiffies here?

This can be called from the watchdog timer.  Timers run in interrupt
context.

-Scott