doc: Add broken-timing possibility to stallwarn.rst

Currently, stallwarn.rst does not mention the fact that timer bugs can
result in false-positive RCU CPU stall warnings.  This commit therefore
adds this to the list.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index 30080ff6f4062d9c11affa57cb56cc1e9afd0285..d1ccd6039a8c3a6b7a90cf6e8f4b61a0a5f43d17 100644 (file)
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -96,6 +96,13 @@ warnings:
        the ``rcu_.*timer wakeup didn't happen for`` console-log message,
        which will include additional debugging information.
 
+-      A timer issue causes time to appear to jump forward, so that RCU
+       believes that the RCU CPU stall-warning timeout has been exceeded
+       when in fact much less time has passed.  This could be due to
+       timer hardware bugs, timer driver bugs, or even corruption of
+       the "jiffies" global variable.  These sorts of timer hardware
+       and driver bugs are not uncommon when testing new hardware.
+
 -      A low-level kernel issue that either fails to invoke one of the
        variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(),
        ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one