Re: [PATCH] virt: kvm: arm: vgic: Return failure code '-EBUSY' when mutex_trylock() fails

Chen Gang
2014-11-13T02:34:14Z

On 11/13/14 3:41, Christoffer Dall wrote:
> On Wed, Nov 12, 2014 at 11:04:23PM +0800, Chen Gang wrote:
>> When mutex_trylock() fails, kvm_vgic_create() will not create 'vgic', so
>> it need return failure code '-EBUSY' instead of '0' to let outside know
>> about it.
>
> I already sent a patch for the -EBUSY:
> https://lists.cs.columbia.edu/pipermail/kvmarm/2014-November/011936.html
>

Yeah, really it is.

>>
>> Also simplify the code within kvm_vgic_create():
>>
>> - kvm_for_each_vcpu() scanning once is enough for current case.
>>
>> - Remove redundant variable 'vcpu_lock_idx'.
>
> I don't like using the iterator variable for this kind of thing because
> it can really break in languages where i is out-of-scope after the loop
> and it is too easy to reuse the iterator variable in later versions of
> the code.
>

For me, what you said is OK, we can still keep it no touch.

> That being said, the scanning once is slightly prettier I guess,
> but I'd rather not introduce the churn unless others (Marc) think this
> is a big win.
>

If only merge the 2 scanning loops, it will not change much. And also
can let code simpler and clearer for readers (both are for processing
and checking '-EBUSY').

If possible, after your patch merges into linux next tree, I will send
the related improving patch for it.

Thanks.

> -Christoffer
>
>>
>>
>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
>> ---
>> virt/kvm/arm/vgic.c | 15 +++++++--------
>> 1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index 3aaca49..5846725 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -1933,7 +1933,7 @@ out:
>>
>> int kvm_vgic_create(struct kvm *kvm)
>> {
>> - int i, vcpu_lock_idx = -1, ret = 0;
>> + int i, ret = 0;
>> struct kvm_vcpu *vcpu;
>>
>> mutex_lock(&kvm->lock);
>> @@ -1949,13 +1949,12 @@ int kvm_vgic_create(struct kvm *kvm)
>> * that no other VCPUs are run while we create the vgic.
>> */
>> kvm_for_each_vcpu(i, vcpu, kvm) {
>> - if (!mutex_trylock(&vcpu->mutex))
>> + if (!mutex_trylock(&vcpu->mutex)) {
>> + ret = -EBUSY;
>> goto out_unlock;
>> - vcpu_lock_idx = i;
>> - }
>> -
>> - kvm_for_each_vcpu(i, vcpu, kvm) {
>> + }
>> if (vcpu->arch.has_run_once) {
>> + mutex_unlock(&vcpu->mutex);
>> ret = -EBUSY;
>> goto out_unlock;
>> }
>> @@ -1968,8 +1967,8 @@ int kvm_vgic_create(struct kvm *kvm)
>> kvm->arch.vgic.vgic_cpu_base = VGIC_ADDR_UNDEF;
>>
>> out_unlock:
>> - for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
>> - vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
>> + while (i-- > 0) {
>> + vcpu = kvm_get_vcpu(kvm, i);
>> mutex_unlock(&vcpu->mutex);
>> }
>>
>> --
>> 1.9.3

--
Chen Gang

Open, share, and attitude like air, water, and life which God blessed