rcu: Provide diagnostic option to slow down grace-period scans
Grace-period scans of the rcu_node combining tree normally
proceed quite quickly, so that it is very difficult to reproduce
races against them. This commit therefore allows grace-period
pre-initialization and cleanup to be artificially slowed down,
increasing race-reproduction probability. A pair of pairs of new
Kconfig parameters are provided, RCU_TORTURE_TEST_SLOW_PREINIT to
enable the slowing down of propagating CPU-hotplug changes up the
combining tree along with RCU_TORTURE_TEST_SLOW_PREINIT_DELAY to
specify the delay in jiffies, and RCU_TORTURE_TEST_SLOW_CLEANUP
to enable the slowing down of the end-of-grace-period cleanup scan
along with RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY to specify the delay
in jiffies. Boot-time parameters named rcutree.gp_preinit_delay and
rcutree.gp_cleanup_delay allow these delays to be specified at boot time.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ba2b0c8..e1af93a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1261,12 +1261,38 @@
Say N here if you want the RCU torture tests to start only
after being manually enabled via /proc.
+config RCU_TORTURE_TEST_SLOW_PREINIT
+ bool "Slow down RCU grace-period pre-initialization to expose races"
+ depends on RCU_TORTURE_TEST
+ help
+ This option delays grace-period pre-initialization (the
+ propagation of CPU-hotplug changes up the rcu_node combining
+ tree) for a few jiffies between initializing each pair of
+ consecutive rcu_node structures. This helps to expose races
+ involving grace-period pre-initialization, in other words, it
+ makes your kernel less stable. It can also greatly increase
+ grace-period latency, especially on systems with large numbers
+ of CPUs. This is useful when torture-testing RCU, but in
+ almost no other circumstance.
+
+ Say Y here if you want your system to crash and hang more often.
+ Say N if you want a sane system.
+
+config RCU_TORTURE_TEST_SLOW_PREINIT_DELAY
+ int "How much to slow down RCU grace-period pre-initialization"
+ range 0 5
+ default 3
+ depends on RCU_TORTURE_TEST_SLOW_PREINIT
+ help
+ This option specifies the number of jiffies to wait between
+ each rcu_node structure pre-initialization step.
+
config RCU_TORTURE_TEST_SLOW_INIT
bool "Slow down RCU grace-period initialization to expose races"
depends on RCU_TORTURE_TEST
help
- This option makes grace-period initialization block for a
- few jiffies between initializing each pair of consecutive
+ This option delays grace-period initialization for a few
+ jiffies between initializing each pair of consecutive
rcu_node structures. This helps to expose races involving
grace-period initialization, in other words, it makes your
kernel less stable. It can also greatly increase grace-period
@@ -1286,6 +1312,30 @@
This option specifies the number of jiffies to wait between
each rcu_node structure initialization.
+config RCU_TORTURE_TEST_SLOW_CLEANUP
+ bool "Slow down RCU grace-period cleanup to expose races"
+ depends on RCU_TORTURE_TEST
+ help
+ This option delays grace-period cleanup for a few jiffies
+ between cleaning up each pair of consecutive rcu_node
+ structures. This helps to expose races involving grace-period
+ cleanup, in other words, it makes your kernel less stable.
+ It can also greatly increase grace-period latency, especially
+ on systems with large numbers of CPUs. This is useful when
+ torture-testing RCU, but in almost no other circumstance.
+
+ Say Y here if you want your system to crash and hang more often.
+ Say N if you want a sane system.
+
+config RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY
+ int "How much to slow down RCU grace-period cleanup"
+ range 0 5
+ default 3
+ depends on RCU_TORTURE_TEST_SLOW_CLEANUP
+ help
+ This option specifies the number of jiffies to wait between
+ each rcu_node structure cleanup operation.
+
config RCU_CPU_STALL_TIMEOUT
int "RCU CPU stall timeout in seconds"
depends on RCU_STALL_COMMON
