RTC revert request

Hey Linus,
Over the holiday break, its been found that a couple of the RTC fixes I
pushed out have been causing worse problems on some hardware then they fix.

Thus, would you please revert:

93b2ec0128c431148b216b8f7337c1a52131ef03
rtc: Expire alarms after the time is set.

and

c0afabd3d553c521e003779c127143ffde55a16f
rtc: Disable the alarm in the hardware

I'll work with the Neil and Rabin to make sure the issues these patches try to address get properly fixed for 3.3.

Sorry again for these late regressions.

Greg: I think you've already picked up "rtc: Disable the alarm in the hardware" and will need to revert that too. Again, my apologies.

thanks
-john

Ok, I picked up on the second revert already because of being cc'd on the discussion about the stable tree.

Can you point me at the background for that first one, or write a changelog for the revert for me? I don't want to have reverts without background and explanation of them..

Linus

Thanks. Sorry for being repetitive, I just wanted to make sure you saw both.

Sure. Here's my assessment of the problem:

	https://lkml.org/lkml/2012/1/3/425

Here's Neil's comments, filling in more on the original issue, as well as his agreement that we should revert for now:

	https://lkml.org/lkml/2012/1/3/454

The basic summary is that we need to ensure that RTC alarms in the past are not added to the timerqueue, or if time is set forward, we properly expire any alarms that are set to the past. Neil's patch does this by scheduling the timer expiry function when we set the RTC time and at initialization, when the hardware alarm could return a value in the past.

Unfortunately, the second case can cause a null pointer dereference if the scheduled work runs prior to us completing the registration function. Since the registration function isn't complete, the we haven't yet returned a valid rtc structure pointer. And the scheduled work may require that pointer.

This issue so far has only cropped up on Xen SMP guests, where registration function takes longer and the scheduled work can quickly run on another cpu before the registration function returns. Regardless its a clear bug.

The right fix is likely to fix the initialization so that we don't use any hardware alarm values that are in the past at registration time. However, such a change will require more testing and this close to a release I'd be more comfortable just reverting the problematic change.

Is that ok for a log?

thanks
-john