linux-kernel - Re: [PATCH] KVM: x86: Kick VCPU outside PIC lock again

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Message-ID: <4B84F9AF.8060804@redhat.com>
Date:	Wed, 24 Feb 2010 12:04:31 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
CC:	Thomas Gleixner <tglx@...utronix.de>, KVM <kvm@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	RT <linux-rt-users@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Kick VCPU outside PIC lock again

On 02/24/2010 11:54 AM, Jan Kiszka wrote:
> Avi Kivity wrote:
>    
>> On 02/24/2010 11:41 AM, Jan Kiszka wrote:
>>      
>>> Thomas Gleixner wrote:
>>>
>>>        
>>>> On Tue, 23 Feb 2010, Jan Kiszka wrote:
>>>>
>>>>
>>>>          
>>>>> Thomas Gleixner wrote:
>>>>>
>>>>>            
>>>>>> The i8254/i8259 locks need to be real spinlocks on preempt-rt. Convert
>>>>>> them to raw_spinlock. No change for !RT kernels.
>>>>>>
>>>>>>              
>>>>> Doesn't fly for -rt anymore: pic_irq_update runs under this raw lock and
>>>>> calls kvm_vcpu_kick which tries to wake_up some thread ->   scheduling
>>>>> while atomic.
>>>>>
>>>>>            
>>>> Hmm, a wakeup itself is fine. Is that code waking a wake queue ?
>>>>
>>>>          
>>> Yes, it's a wake queue.
>>>
>>>        
>> So what's the core issue?  Is the lock_t in the wait_queue a sleeping mutex?
>>      
> Yep.
>    

I see.  Won't we hit the same issue when we call pic functions from 
atomic context during the guest entry sequence?

-- 
error compiling committee.c: too many arguments to function

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