From: Steven Rostedtrostedt@goodmis.org <rostedt@goodmis.org>

CPU0 expires a posix-timer and runs the callback function.  The signal is
queued.

After releasing the posix-timer lock and before returning to hrtimer_run_queue
CPU0 gets interrupted.  CPU1 delivers the queued signal and rearms the timer.
CPU0 comes back to hrtimer_run_queue and sets the timer state to expired.

The next modification of the timer can result in an oops, because the state
information is wrong.

Keep track of state = RUNNING and check if the state has been in the return
path of hrtimer_run_queue.  In case the state has been changed, ignore a
restart request and do not touch the state variable.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>