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-rw-r--r--Documentation/RCU/stallwarn.rst23
1 files changed, 22 insertions, 1 deletions
diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index c9ab6af4d3be..d53856cc6390 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -92,7 +92,9 @@ warnings:
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.
+ yes, even including bugs in RCU itself. It can also result in
+ the ``rcu_.*timer wakeup didn't happen for`` console-log message,
+ which will include additional debugging information.
- A bug in the RCU implementation.
@@ -292,6 +294,25 @@ kthread is waiting for a short timeout, the "state" precedes value of the
task_struct ->state field, and the "cpu" indicates that the grace-period
kthread last ran on CPU 5.
+If the relevant grace-period kthread does not wake from FQS wait in a
+reasonable time, then the following additional line is printed::
+
+ kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
+
+The "23804" indicates that kthread's timer expired more than 23 thousand
+jiffies ago. The rest of the line has meaning similar to the kthread
+starvation case.
+
+Additionally, the following line is printed::
+
+ Possible timer handling issue on cpu=4 timer-softirq=11142
+
+Here "cpu" indicates that the grace-period kthread last ran on CPU 4,
+where it queued the fqs timer. The number following the "timer-softirq"
+is the current ``TIMER_SOFTIRQ`` count on cpu 4. If this value does not
+change on successive RCU CPU stall warnings, there is further reason to
+suspect a timer problem.
+
Multiple Warnings From One Stall
================================