doc: Timer problems can cause RCU CPU stall warnings

Over the past few years, there have been several cases where timekeeping
bugs have caused RCU CPU stall warnings, particularly during hardware
bringup.  This commit therefore adds such bugs to the list of things
that can result in RCU CPU stall warnings.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
1 file changed