[RFC PATCH 1/7] rcu: correct CONFIG_EXT_RCU_CPU_STALL_TIMEOUT descriptions

[Robert Elliott]

Make the descriptions of CONFIG_EXT_RCU_CPU_STALL_TIMEOUT
match the code:

- there is no longer a default of 20 ms for Android since
commit 1045a06724f3 ("remove CONFIG_ANDROID"),

- the code includes a maximum of 21 seconds, evident when
specifying 0 which means to use the CONFIG_RCU_STALL_TIMEOUT
value (whose default is 60 seconds).

Example .config:
  CONFIG_RCU_CPU_STALL_TIMEOUT=60
  CONFIG_RCU_EXP_CPU_STALL_TIMEOUT=0

leads to:
  /sys/module/rcupdate/parameters/rcu_cpu_stall_timeout:60
  /sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout:21000

Fixes: 1045a06724f3 ("remove CONFIG_ANDROID")
Signed-off-by: Robert Elliott <elliott@xxxxxxx>
---
 Documentation/RCU/stallwarn.rst | 9 +++++----
 kernel/rcu/Kconfig.debug        | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index e38c587067fc..d86a8b47504f 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -168,10 +168,11 @@ CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
 	Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for
 	the expedited grace period. This parameter defines the period
 	of time that RCU will wait from the beginning of an expedited
-	grace period until it issues an RCU CPU stall warning. This time
-	period is normally 20 milliseconds on Android devices.	A zero
-	value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used,
-	after conversion to milliseconds.
+	grace period until it issues an RCU CPU stall warning.
+
+	A zero value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be
+        used, after conversion to milliseconds, limited to a maximum of
+        21 seconds.
 
 	This configuration parameter may be changed at runtime via the
 	/sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 1b0c41d490f0..4477eeb8a54f 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -93,7 +93,7 @@ config RCU_EXP_CPU_STALL_TIMEOUT
 	  If the RCU grace period persists, additional CPU stall warnings
 	  are printed at more widely spaced intervals.  A value of zero
 	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
-	  seconds to milliseconds.
+	  seconds to milliseconds, limited to a maximum of 21 seconds.
 
 config RCU_TRACE
 	bool "Enable tracing for RCU"
-- 
2.37.3