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

[mirror_ubuntu-bionic-kernel.git] / Documentation / RCU / stallwarn.txt

diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 96a3d81837e1b120098eccfd1b95b0bfc4947be9..21b8913acbdfc405461caa5cb14b89c05991000c 100644 (file)
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -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