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

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Message-ID: <4B84F5D4.5020202@redhat.com>
Date:	Wed, 24 Feb 2010 11:48:04 +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 11:41 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?

> This restores the deferred VCPU kicking before 956f97cf. We need this
> over -rt as wake_up* requires non-atomic context in this configuration.
>
>    

Seems sane, will apply once I understand why the current code fails.

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

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