rcu: Provide diagnostic option to slow down grace-period initialization

Grace-period initialization normally proceeds quite quickly, so
that it is very difficult to reproduce races against grace-period
initialization.  This commit therefore allows grace-period
initialization to be artificially slowed down, increasing
race-reproduction probability.  A pair of new Kconfig parameters are
provided, CONFIG_RCU_TORTURE_TEST_SLOW_INIT to enable the slowdowns, and
CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY to specify the number of jiffies
of slowdown to apply.  A boot-time parameter named rcutree.gp_init_delay
allows boot-time delay to be specified.  By default, no delay will be
applied even if CONFIG_RCU_TORTURE_TEST_SLOW_INIT is set.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a62a7b4..94de410ec341 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2968,6 +2968,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         Set maximum number of finished RCU callbacks to
                         process in one batch.
 
+        rcutree.gp_init_delay=  [KNL]
+                        Set the number of jiffies to delay each step of
+                        RCU grace-period initialization.  This only has
+                        effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT is
+                        set.
+
         rcutree.rcu_fanout_leaf= [KNL]
                         Increase the number of CPUs assigned to each
                         leaf rcu_node structure.  Useful for very large