linux-kernel - Re: [RFC 01/12] KVM: arm/arm64: Avoid multiple dist->spis kfree

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Date:   Mon, 19 Mar 2018 21:51:10 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>, eric.auger.pro@...il.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, cdall@...nel.org,
        peter.maydell@...aro.org
Cc:     andre.przywara@....com, drjones@...hat.com, wei@...hat.com
Subject: Re: [RFC 01/12] KVM: arm/arm64: Avoid multiple dist->spis kfree

Hi Marc,

On 19/03/18 14:46, Marc Zyngier wrote:
> On 19/03/18 09:20, Eric Auger wrote:
>> in case kvm_vgic_map_resources() fails, typically if the vgic
>> distributor is not defined, __kvm_vgic_destroy will be called
>> several times. Indeed kvm_vgic_map_resources() is called on
>> first vcpu run. As a result dist->spis is freeed twice and on
>> the second time it causes a "kernel BUG at mm/slub.c:3912!"
>>
>> This patch avoids freeing dist->spis twice.
>>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>> ---
>>  virt/kvm/arm/vgic/vgic-init.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
>> index 743ca5c..38fd5f1 100644
>> --- a/virt/kvm/arm/vgic/vgic-init.c
>> +++ b/virt/kvm/arm/vgic/vgic-init.c
>> @@ -324,7 +324,10 @@ static void kvm_vgic_dist_destroy(struct kvm *kvm)
>>  	dist->ready = false;
>>  	dist->initialized = false;
>>  
>> -	kfree(dist->spis);
>> +	if (dist->spis) {
>> +		kfree(dist->spis);
>> +		dist->spis = NULL;
>> +	}
> 
> Given that kfree(NULL) is always a valid thing to do, you could write
> the same thing just as
> 
> 	dist-> spis = NULL;
> 
> without any test.
sure
> 
>>  	dist->nr_spis = 0;
>>  
>>  	if (vgic_supports_direct_msis(kvm))
>>
> 
> You also may want to add a Fixes tag to it.
OK

Thanks

Eric
> 
> Thanks,
> 
> 	M.
>