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 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

			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

kernel/rcu/tree.c

+10 −0
Original line number 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;

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);

lib/Kconfig.debug

+24 −0
Original line number 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

	  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

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