Re: [PATCH 2/4] alarmtimer: Make alarmtimer platform device child of RTC device

From: Doug Anderson
Date: Wed Jan 15 2020 - 14:22:43 EST


Hi,

On Wed, Jan 15, 2020 at 2:07 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> Doug Anderson <dianders@xxxxxxxxxxxx> writes:
> > On Thu, Jan 9, 2020 at 7:59 AM Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
> >> diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
> >> index 4b11f0309eee..ccb6aea4f1d4 100644
> >> --- a/kernel/time/alarmtimer.c
> >> +++ b/kernel/time/alarmtimer.c
> >> @@ -88,6 +88,7 @@ static int alarmtimer_rtc_add_device(struct device *dev,
> >> unsigned long flags;
> >> struct rtc_device *rtc = to_rtc_device(dev);
> >> struct wakeup_source *__ws;
> >> + struct platform_device *pdev;
> >> int ret = 0;
> >>
> >> if (rtcdev)
> >> @@ -99,6 +100,7 @@ static int alarmtimer_rtc_add_device(struct device *dev,
> >> return -1;
> >>
> >> __ws = wakeup_source_register(dev, "alarmtimer");
> >> + pdev = platform_device_register_data(dev, "alarmtimer", -1, NULL, 0);
> >
> > Don't you need to check for an error here? If pdev is an error you'll
> > continue on your merry way. Before your patch if you got an error
> > registering the device it would have caused probe to fail.
>
> Yes, that return value should be checked
>
> > I guess you'd only want it to be an error if "rtcdev" is NULL?
>
> If rtcdev is not NULL then this code is not reached. See the begin of
> this function :)

Wow, not sure how I missed that. I guess the one at the top of the
function is an optimization, though? It's being accessed without the
spinlock which means that it's not necessarily reliable, right? I
guess once the rtcdev has been set then it is never unset, but it does
seem like if two threads could call alarmtimer_rtc_add_device() at the
same time then it's possible that we could end up calling
wakeup_source_register() for both of them. Did I understand that
correctly? If I did then maybe it deserves a comment?

-Doug