Re: [Xen-devel] [PATCH v11 5/9] x86: dynamically attach/detach QoS monitoring service for a guest

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.06.14 at 16:31, <dongxiao.xu@xxxxxxxxx> wrote:
> +int pqos_monitor_alloc_rmid(struct domain *d)
> +{
> +    int rc = 0;
> +    unsigned int rmid;
> +
> +    ASSERT(pqos_monitor_enabled());
> +
> +    spin_lock(&pqosm->pqosm_lock);
> +
> +    if ( d->arch.pqos_rmid > 0 )
> +    {
> +        rc = -EEXIST;
> +        goto out;
> +    }

Does this check really need to be inside the locked region? You're
already protected against races by the domctl lock.

> +void pqos_monitor_free_rmid(struct domain *d)
> +{
> +    unsigned int rmid;
> +
> +    spin_lock(&pqosm->pqosm_lock);
> +    rmid = d->arch.pqos_rmid;
> +    /* We do not free system reserved "RMID=0" */
> +    if ( rmid == 0 )
> +        goto out;

Similarly here.

Jan


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