Re: [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep

James Morse
2023-04-27T14:16:17Z

Hi Reinette,

On 01/04/2023 00:26, Reinette Chatre wrote:
> On 3/20/2023 10:26 AM, James Morse wrote:
>
> ...
>
>> int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>> u32 closid, u32 rmid, enum resctrl_event_id eventid,
>> u64 *val)
>> {
>> struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>> struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
>> + struct __rmid_read_arg arg;
>> struct arch_mbm_state *am;
>> u64 msr_val, chunks;
>> - int ret;
>> + int err;
>>
>> - if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
>> - return -EINVAL;
>> + arg.rmid = rmid;
>> + arg.eventid = eventid;
>>
>> - ret = __rmid_read(rmid, eventid, &msr_val);
>> - if (ret)
>> - return ret;
>> + err = smp_call_function_any(&d->cpu_mask, smp_call_rmid_read, &arg, true);
>> + if (err)
>> + return err;
>
> This seems to break the assumption of expected return values. __mon_event_count()
> does:
> rr->err = resctrl_arch_rmid_read()
>
> and later rdtgroup_mondata_show() only expects -EIO or -EINVAL as errors, with
> default of success.

Yes, looks like I dithered on whether cpus_read_lock() should be held over this function,
or it should tolerate the error. This is protected by rdtgroup_mutex, which means the
hotplug callbacks can't run concurrently, so the error can't occur.

I'll change it to ignore the return value.

Thanks,

James