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.
> >> @@ -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) {
> >> + 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?
Alan Stern
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