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

Christoffer Dall
2014-11-12T19:41:44Z

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

>
> 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.

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.

-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