Re: [PATCH v2 2/3] xen/sched: carve out memory allocation and freeing from schedule_cpu_rm()

[Jan Beulich <jbeulich@suse.com>]

On 15.08.2022 13:04, Juergen Gross wrote:
> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -3237,6 +3237,65 @@ out:
>      return ret;
>  }
>  
> +static struct cpu_rm_data *schedule_cpu_rm_alloc(unsigned int cpu)
> +{
> +    struct cpu_rm_data *data;
> +    const struct sched_resource *sr;
> +    unsigned int idx;
> +
> +    rcu_read_lock(&sched_res_rculock);
> +
> +    sr = get_sched_res(cpu);
> +    data = xmalloc_flex_struct(struct cpu_rm_data, sr, sr->granularity - 1);
> +    if ( !data )
> +        goto out;
> +
> +    data->old_ops = sr->scheduler;
> +    data->vpriv_old = idle_vcpu[cpu]->sched_unit->priv;
> +    data->ppriv_old = sr->sched_priv;

Repeating a v1 comment:

"At least from an abstract perspective, doesn't reading fields from
 sr require the RCU lock to be held continuously (i.e. not dropping
 it at the end of this function and re-acquiring it in the caller)?"

Initially I thought you did respond to this in some way, but when
looking for a matching reply I couldn't find one.

Jan