On 10/08/2015 02:20 PM, Alan Stern wrote:
> On Thu, 8 Oct 2015, Grygorii Strashko wrote:
>
>>>> /**
>>>> + * device_defer_all_probes() - Enable/disable probing of devices
>>>> + * @enable: Enable/disable probing of devices
>>>> + *
>>>> + * if @enable = true
>>>> + * It will disable probing of devices and defer their probes.
>>>> + * otherwise
>>>> + * It will restore normal behavior and trigger re-probing of
>>>> deferred
>>>> + * devices.
>>>> + */
>>>> +void device_defer_all_probes(bool enable)
>>>> +{
>>>> + defer_all_probes = enable;
>>>> + if (enable)
>>>> + /* sync with probes to avoid any races. */
>>>> + wait_for_device_probe();
>>
>> ^ pls, pay attention on above code line
>>
>>>> + else
>>>> + driver_deferred_probe_trigger();
>>>> +}
>>>
>>> Some people might prefer to see two separate functions, an enable
>>> routine and a disable routine. I don't much care.
>>
>> May be. Should I change it?
>
> It would then be more in line with functions like
> pm_runtime_set_{active|suspended} or pm_runtime_[dont_]use_autosuspend.
ok
>
>>>> @@ -277,9 +304,15 @@ static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
>>>>
>>>> static int really_probe(struct device *dev, struct device_driver *drv)
>>>> {
>>>> - int ret = 0;
>>>> + int ret = -EPROBE_DEFER;
>>>> int local_trigger_count = atomic_read(&deferred_trigger_count);
>>>>
>>>> + if (defer_all_probes) {
Will it be ok If I add below comment here?
/*
* Value of defer_all_probes can be set only by
* device_defer_all_probes_enable() which, in turn, will call
* wait_for_device_probe() right after that to avoid any races.
*/
>>>> + dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
>>>> + driver_deferred_probe_add(dev);
>>>> + return ret;
>>>> + }
>>>
>>> In theory there's a race here. If one CPU sets defer_all_probes, the
>>> new value might not be perceived by another CPU until a little while
>>> later. Is there an easy way to insure that this race won't cause any
>>> problems?
>>
>> Yes. this question was raised by Rafael also [1].
>
> I see. Can you add a comment explaining all of this?
--
regards,
-grygorii
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