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

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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>
This commit is contained in:
Paul E. McKenney
2015-01-22 18:24:08 -08:00
parent 237a0f2193
commit 37745d2810
3 changed files with 40 additions and 0 deletions
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6
Documentation/kernel-parameters.txt
View File

@@ -2968,6 +2968,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Set maximum number of finished RCU callbacks to Set maximum number of finished RCU callbacks to
process in one batch. 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] rcutree.rcu_fanout_leaf= [KNL]
Increase the number of CPUs assigned to each Increase the number of CPUs assigned to each
leaf rcu_node structure. Useful for very large leaf rcu_node structure. Useful for very large

10
kernel/rcu/tree.c
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@@ -160,6 +160,12 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO; static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
module_param(kthread_prio, int, 0644); module_param(kthread_prio, int, 0644);
/* Delay in jiffies for grace-period initialization delays. */
static int gp_init_delay = IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT)
? CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY
: 0;
module_param(gp_init_delay, int, 0644);
/* /*
* Track the rcutorture test sequence number and the update version * Track the rcutorture test sequence number and the update version
* number within a given test. The rcutorture_testseq is incremented * number within a given test. The rcutorture_testseq is incremented
@@ -1769,6 +1775,10 @@ static int rcu_gp_init(struct rcu_state *rsp)
raw_spin_unlock_irq(&rnp->lock); raw_spin_unlock_irq(&rnp->lock);
cond_resched_rcu_qs(); cond_resched_rcu_qs();
ACCESS_ONCE(rsp->gp_activity) = jiffies; ACCESS_ONCE(rsp->gp_activity) = jiffies;
if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_SLOW_INIT) &&
gp_init_delay > 0 &&
!(rsp->gpnum % (rcu_num_nodes * 10)))
schedule_timeout_uninterruptible(gp_init_delay);
} }
mutex_unlock(&rsp->onoff_mutex); mutex_unlock(&rsp->onoff_mutex);

24
lib/Kconfig.debug
View File

@@ -1257,6 +1257,30 @@ config RCU_TORTURE_TEST_RUNNABLE
Say N here if you want the RCU torture tests to start only Say N here if you want the RCU torture tests to start only
after being manually enabled via /proc. after being manually enabled via /proc.
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
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
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_INIT_DELAY
int "How much to slow down RCU grace-period initialization"
range 0 5
default 0
help
This option specifies the number of jiffies to wait between
each rcu_node structure initialization.
config RCU_CPU_STALL_TIMEOUT config RCU_CPU_STALL_TIMEOUT
int "RCU CPU stall timeout in seconds" int "RCU CPU stall timeout in seconds"
depends on RCU_STALL_COMMON depends on RCU_STALL_COMMON