documentation: Describe new expedited stall warnings

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 046f32637b95a8813d12d0178dc1270bfc62a5c8..efb9454875ab7453255532887225ad0cb2d5d2fd 100644 (file)
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -163,6 +163,23 @@ message will be about three times the interval between the beginning
 of the stall and the first message.
 
 
 of the stall and the first message.
 
 

+Stall Warnings for Expedited Grace Periods
+
+If an expedited grace period detects a stall, it will place a message
+like the following in dmesg:
+
+       INFO: rcu_sched detected expedited stalls on CPUs: { 1 2 6 } 26009 jiffies s: 1043
+
+This indicates that CPUs 1, 2, and 6 have failed to respond to a
+reschedule IPI, that the expedited grace period has been going on for
+26,009 jiffies, and that the expedited grace-period sequence counter is
+1043.  The fact that this last value is odd indicates that an expedited
+grace period is in flight.
+
+It is entirely possible to see stall warnings from normal and from
+expedited grace periods at about the same time from the same run.
+
+

 What Causes RCU CPU Stall Warnings?
 
 So your kernel printed an RCU CPU stall warning.  The next question is
 What Causes RCU CPU Stall Warnings?
 
 So your kernel printed an RCU CPU stall warning.  The next question is