[PATCH RFC tip/core/rcu 09/28] rcu: Document failing tick as cause of RCU CPU stall warning

[Paul E. McKenney]

One of lclaudio's systems was seeing RCU CPU stall warnings from idle.
These turned out to be caused by a bug that stopped scheduling-clock
tick interrupts from being sent to a given CPU for several hundred seconds.
This commit therefore updates the documentation to call this out as a
possible cause for RCU CPU stall warnings.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 Documentation/RCU/stallwarn.txt |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 4e95920..f3e0625 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -101,6 +101,11 @@ o	A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
 	CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning
 	messages.
 
+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
+	result in RCU CPU stall warnings for CONFIG_NO_HZ=n kernels.
+
 o	A bug in the RCU implementation.
 
 o	A hardware failure.  This is quite unlikely, but has occurred
-- 
1.7.3.2

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