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documentation: Long-running irq handlers can stall RCU grace periods

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If a periodic interrupt's handler takes longer to execute than the period
between successive interrupts, RCU's kthreads and softirq handlers can
be prevented from executing, resulting in otherwise inexplicable RCU
CPU stall warnings.  This commit therefore calls out this possibility
in Documentation/RCU/stallwarn.txt.

Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-08-09 10:16:29 -07:00
parent bb7e5ce7dd
commit dfa0ee48ef
1 changed files with 11 additions and 1 deletions
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12
Documentation/RCU/stallwarn.txt
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@ -40,7 +40,9 @@ o Booting Linux using a console connection that is too slow to
o Anything that prevents RCU's grace-period kthreads from running.
This can result in the "All QSes seen" console-log message.
This message will include information on when the kthread last
ran and how often it should be expected to run.
ran and how often it should be expected to run. It can also
result in the "rcu_.*kthread starved for" console-log message,
which will include additional debugging information.
o A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
happen to preempt a low-priority task in the middle of an RCU
@ -60,6 +62,14 @@ o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
CONFIG_PREEMPT_RCU case, you might see stall-warning
messages.
o A periodic interrupt whose handler takes longer than the time
interval between successive pairs of interrupts. This can
prevent RCU's kthreads and softirq handlers from running.
Note that certain high-overhead debugging options, for example
the function_graph tracer, can result in interrupt handler taking
considerably longer than normal, which can in turn result in
RCU CPU stall warnings.
o A hardware or software issue shuts off the scheduler-clock
interrupt on a CPU that is not in dyntick-idle mode. This
problem really has happened, and seems to be most likely to