> -----Original Message-----
> From: Thomas Gleixner [mailto:t...@linutronix.de]
> Sent: Friday, November 02, 2012 6:56 AM
> To: Liu, Chuansheng
> Cc: john.stu...@linaro.org; gre...@linuxfoundation.org;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 2/3] alarmtimer: Using the alarmtimer_get_rtcdev for all
> posix clock interface
>
> On Thu, 1 Nov 2012, Chuansheng Liu wrote:
> >
> > Some posix clock interface directly use the variable rtcdev,
> > cleanup it here by alarmtimer_get_rtcdev().
> >
> > Signed-off-by: liu chuansheng <chuansheng....@intel.com>
> > ---
> > kernel/time/alarmtimer.c | 13 ++++++-------
> > 1 files changed, 6 insertions(+), 7 deletions(-)
> >
> > diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
> > index 4fc17cb..5490fa8 100644
> > --- a/kernel/time/alarmtimer.c
> > +++ b/kernel/time/alarmtimer.c
> > @@ -86,11 +86,10 @@ static int alarmtimer_rtc_add_device(struct device
> *dev,
> > return -1;
> >
> > mutex_lock(&rtcdev_mutex);
> > - if (!rtcdev) {
> > - rtcdev = rtc;
> > - /* hold a reference so it doesn't go away */
> > - get_device(dev);
> > - }
> > + rtcdev = rtc;
> > + /* hold a reference so it doesn't go away */
> > + get_device(dev);
> > +
>
> Brilliant.
>
> rtcdev = NULL
>
> CPU0 CPU 1
>
> alarmtimer_rtc_add_device(A)
> if (rtcdev) alarmtimer_rtc_add_device(B)
> return -EBUSY; if (rtcdev)
> mutex_lock(); return -EBUSY;
> rtcdev = A; mutex_lock();
> mutex_unlock;
>
> bla = alarmtimer_rtc_get_device()
>
> So bla = A
> mutex_lock() returns
> rtcdev = B;
> mutex_unlock();
>
> The next call to alarmtimer_rtc_get_device() will return B. Not what
> you want. Maybe you want that, but then your patch is missing an
> explanation why you want that and why this would be a desired
> behaviour.
Thanks your pointing out, I am wrong.
>
> Thanks,
>
> tglx
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