hrtimer: Prevent all reprogramming if hang detected

If the last hrtimer interrupt detected a hang it sets hang_detected=1
and programs the clock event device with a delay to let the system
make progress.

If hang_detected == 1, we prevent reprogramming of the clock event
device in hrtimer_reprogram() but not in hrtimer_force_reprogram().

This can lead to the following situation:

hrtimer_interrupt()
   hang_detected = 1;
   program ce device to Xms from now (hang delay)

We have two timers pending:
   T1 expires 50ms from now
   T2 expires 5s from now

Now T1 gets canceled, which causes hrtimer_force_reprogram() to be
invoked, which in turn programs the clock event device to T2 (5
seconds from now).

Any hrtimer_start after that will not reprogram the hardware due to
hang_detected still being set. So we effectivly block all timers until
the T2 event fires and cleans up the hang situation.

Add a check for hang_detected to hrtimer_force_reprogram() which
prevents the reprogramming of the hang delay in the hardware
timer. The subsequent hrtimer_interrupt will resolve all outstanding
issues.

[ tglx: Rewrote subject and changelog and fixed up the comment in
  	hrtimer_force_reprogram() ]

Change-Id: I3f8906cb60ec34390fce7c4056a5514a724b0705
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Link: http://lkml.kernel.org/r/53602DC6.2060101@gmail.com


Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Git-commit: 6c6c0d5a1c949d2e084706f9e5fb1fccc175b265
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


Signed-off-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>
Signed-off-by: Bharat Pawar <bpawar@codeaurora.org>
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>