Re: [PATCH] kvmppc_init_timing_stats: fix sleep with interrupts disabled

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

On 10/01/2010 12:07 AM, Alexander Graf wrote:
>
> On 30.09.2010, at 21:28, Scott Wood wrote:
>
>> It is not legal to call mutex_lock() with interrupts disabled.
>> This will assert with debug checks enabled.
>>
>> If there's a real need to disable interrupts here, it could be done
>> after the mutex is acquired -- but I don't see why it's needed at all.
>
> Christian, IIRC this code is yours. Any comments?

Yes, It should be save to drop the irq_disable.
IIRC it was without the lock in early stages of development (pre 
upstream git, so you can't see it) which had some obvious races.
But the lock makes it mutually exclusive per vcpu and should ensure it 
isn't running - by that it should be fine.

Reviewed-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>

> Alex
>
>>
>> Signed-off-by: Scott Wood<scottwood@freescale.com>
>> ---
>> arch/powerpc/kvm/timing.c |    2 --
>> 1 files changed, 0 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/timing.c b/arch/powerpc/kvm/timing.c
>> index 46fa04f..a021f58 100644
>> --- a/arch/powerpc/kvm/timing.c
>> +++ b/arch/powerpc/kvm/timing.c
>> @@ -35,7 +35,6 @@ void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
>> 	int i;
>>
>> 	/* pause guest execution to avoid concurrent updates */
>> -	local_irq_disable();
>> 	mutex_lock(&vcpu->mutex);
>>
>> 	vcpu->arch.last_exit_type = 0xDEAD;
>> @@ -51,7 +50,6 @@ void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
>> 	vcpu->arch.timing_last_enter.tv64 = 0;
>>
>> 	mutex_unlock(&vcpu->mutex);
>> -	local_irq_enable();
>> }
>>
>> static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
>> --
>> 1.7.0.4
>>
>> --
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>

-- 

Grüsse / regards, Christian Ehrhardt
IBM Linux Technology Center, System z Linux Performance