Re: [PATCH v3 2/4] PM / QoS: add lockless read for flags

[Kevin Hilman]

"Rafael J. Wysocki (Intel)" <rafael@xxxxxxxxxx> writes:

> On Thu, Jun 11, 2026 at 9:59 PM Kevin Hilman (TI) <khilman@xxxxxxxxxxxx> wrote:
>>
>> Add a lockless read for QoS flags similar to the lockless read for
>> resume latency (dev_pm_qos_raw_resume_latency) which may be called
>> from atomic context (e.g. genpd governors running under a raw spinlock
>> or in the syscore suspend path), where taking that sleeping lock would
>> be invalid on PREEMPT_RT.
>>
>> Signed-off-by: Kevin Hilman (TI) <khilman@xxxxxxxxxxxx>
>> ---
>>  include/linux/pm_qos.h | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
>> index aededda52b6b..439a9e779d81 100644
>> --- a/include/linux/pm_qos.h
>> +++ b/include/linux/pm_qos.h
>> @@ -219,6 +219,12 @@ static inline s32 dev_pm_qos_raw_resume_latency(struct device *dev)
>>                 PM_QOS_RESUME_LATENCY_NO_CONSTRAINT :
>>                 pm_qos_read_value(&dev->power.qos->resume_latency);
>>  }
>> +
>> +static inline s32 dev_pm_qos_raw_flags(struct device *dev)
>> +{
>> +       return IS_ERR_OR_NULL(dev->power.qos) ?
>> +               0 : READ_ONCE(dev->power.qos->flags.effective_flags);
>
> So if you add READ_ONCE() on the reader side, all updates of it need
> to go under WRITE_ONCE(), or the READ_ONCE() may still not be
> effective.
>
> I don't think they are under WRITE_ONCE() ATM.

Ah, good catch.  Thanks for the review, I'll fix that in v4.

Kevin