Commit-ID: 37745d281069682d901f00c0121949a7d224195f Gitweb: http://git.kernel.org/tip/37745d281069682d901f00c0121949a7d224195f Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Thu, 22 Jan 2015 18:24:08 -0800 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Wed, 11 Mar 2015 13:22:38 -0700 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@xxxxxxxxxxxxxxxxxx> --- Documentation/kernel-parameters.txt | 6 ++++++ kernel/rcu/tree.c | 10 ++++++++++ lib/Kconfig.debug | 24 ++++++++++++++++++++++++ 3 files changed, 40 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index bfcb1a6..94de410 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 diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 3b7e413..b42001f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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; 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 * 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); cond_resched_rcu_qs(); 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); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index c5cefb3..feee8da 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1257,6 +1257,30 @@ config RCU_TORTURE_TEST_RUNNABLE Say N here if you want the RCU torture tests to start only 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 int "RCU CPU stall timeout in seconds" depends on RCU_STALL_COMMON -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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