problem really has happened, and seems to be most likely to
result in RCU CPU stall warnings for CONFIG_NO_HZ_COMMON=n kernels.
+- A hardware or software issue that prevents time-based wakeups
+ from occurring. These issues can range from misconfigured or
+ buggy timer hardware through bugs in the interrupt or exception
+ path (whether hardware, firmware, or software) through bugs
+ in Linux's timer subsystem through bugs in the scheduler, and,
+ yes, even including bugs in RCU itself.
+
- A bug in the RCU implementation.
- A hardware failure. This is quite unlikely, but has occurred