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Commit 37745d28 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 237a0f21

Documentation/kernel-parameters.txt

+6 −0
Original line number Original line Diff line number Diff line
@@ -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

kernel/rcu/tree.c

+10 −0
Original line number Original line Diff line number Diff line
@@ -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);

lib/Kconfig.debug

+24 −0
Original line number Original line Diff line number Diff line
@@ -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