Commit 38706bc5 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcutorture: Add callback-flood test 



Although RCU is designed to handle arbitrary floods of callbacks, this
capability is not routinely tested.   This commit therefore adds a
cbflood capability in which kthreads repeatedly registers large numbers
of callbacks.  One such kthread is created for each four CPUs (rounding
up), and the test may be controlled by several cbflood_* kernel boot
parameters, which control the number of bursts per flood, the number
of callbacks per burst, the time between bursts, and the time between
floods.  The default values are large enough to exercise RCU's emergency
responses to callback flooding.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Miller <davem@davemloft.net>
Reviewed-by: default avatarPranith Kumar <bobby.prani@gmail.com>
parent eea203fe

Documentation/kernel-parameters.txt

+18 −0
Original line number Diff line number Diff line
@@ -2881,6 +2881,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Lazy RCU callbacks are those which RCU can

			prove do nothing more than free memory.



	rcutorture.cbflood_inter_holdoff= [KNL]

			Set holdoff time (jiffies) between successive

			callback-flood tests.



	rcutorture.cbflood_intra_holdoff= [KNL]

			Set holdoff time (jiffies) between successive

			bursts of callbacks within a given callback-flood

			test.



	rcutorture.cbflood_n_burst= [KNL]

			Set the number of bursts making up a given

			callback-flood test.  Set this to zero to

			disable callback-flood testing.



	rcutorture.cbflood_n_per_burst= [KNL]

			Set the number of callbacks to be registered

			in a given burst of a callback-flood test.



	rcutorture.fqs_duration= [KNL]

			Set duration of force_quiescent_state bursts.

kernel/rcu/rcutorture.c

+85 −1
Original line number Diff line number Diff line
@@ -49,11 +49,19 @@ 
#include <linux/trace_clock.h>

#include <asm/byteorder.h>

#include <linux/torture.h>

#include <linux/vmalloc.h>



MODULE_LICENSE("GPL");

MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and Josh Triplett <josh@joshtriplett.org>");





torture_param(int, cbflood_inter_holdoff, HZ,

	      "Holdoff between floods (jiffies)");

torture_param(int, cbflood_intra_holdoff, 1,

	      "Holdoff between bursts (jiffies)");

torture_param(int, cbflood_n_burst, 3, "# bursts in flood, zero to disable");

torture_param(int, cbflood_n_per_burst, 20000,

	      "# callbacks per burst in flood");

torture_param(int, fqs_duration, 0,

	      "Duration of fqs bursts (us), 0 to disable");

torture_param(int, fqs_holdoff, 0, "Holdoff time within fqs bursts (us)");
@@ -96,10 +104,12 @@ module_param(torture_type, charp, 0444); 
MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, ...)");



static int nrealreaders;

static int ncbflooders;

static struct task_struct *writer_task;

static struct task_struct **fakewriter_tasks;

static struct task_struct **reader_tasks;

static struct task_struct *stats_task;

static struct task_struct **cbflood_task;

static struct task_struct *fqs_task;

static struct task_struct *boost_tasks[NR_CPUS];

static struct task_struct *stall_task;
@@ -138,6 +148,7 @@ static long n_rcu_torture_boosts; 
static long n_rcu_torture_timers;

static long n_barrier_attempts;

static long n_barrier_successes;

static atomic_long_t n_cbfloods;

static struct list_head rcu_torture_removed;



static int rcu_torture_writer_state;
@@ -707,6 +718,58 @@ checkwait: stutter_wait("rcu_torture_boost"); 
	return 0;

}



static void rcu_torture_cbflood_cb(struct rcu_head *rhp)

{

}



/*

 * RCU torture callback-flood kthread.  Repeatedly induces bursts of calls

 * to call_rcu() or analogous, increasing the probability of occurrence

 * of callback-overflow corner cases.

 */

static int

rcu_torture_cbflood(void *arg)

{

	int err = 1;

	int i;

	int j;

	struct rcu_head *rhp;



	if (cbflood_n_per_burst > 0 &&

	    cbflood_inter_holdoff > 0 &&

	    cbflood_intra_holdoff > 0 &&

	    cur_ops->call &&

	    cur_ops->cb_barrier) {

		rhp = vmalloc(sizeof(*rhp) *

			      cbflood_n_burst * cbflood_n_per_burst);

		err = !rhp;

	}

	if (err) {

		VERBOSE_TOROUT_STRING("rcu_torture_cbflood disabled: Bad args or OOM");

		while (!torture_must_stop())

			schedule_timeout_interruptible(HZ);

		return 0;

	}

	VERBOSE_TOROUT_STRING("rcu_torture_cbflood task started");

	do {

		schedule_timeout_interruptible(cbflood_inter_holdoff);

		atomic_long_inc(&n_cbfloods);

		WARN_ON(signal_pending(current));

		for (i = 0; i < cbflood_n_burst; i++) {

			for (j = 0; j < cbflood_n_per_burst; j++) {

				cur_ops->call(&rhp[i * cbflood_n_per_burst + j],

					      rcu_torture_cbflood_cb);

			}

			schedule_timeout_interruptible(cbflood_intra_holdoff);

			WARN_ON(signal_pending(current));

		}

		cur_ops->cb_barrier();

		stutter_wait("rcu_torture_cbflood");

	} while (!torture_must_stop());

	torture_kthread_stopping("rcu_torture_cbflood");

	return 0;

}



/*

 * RCU torture force-quiescent-state kthread.  Repeatedly induces

 * bursts of calls to force_quiescent_state(), increasing the probability
@@ -1075,10 +1138,11 @@ rcu_torture_stats_print(void) 
		n_rcu_torture_boosts,

		n_rcu_torture_timers);

	torture_onoff_stats();

	pr_cont("barrier: %ld/%ld:%ld\n",

	pr_cont("barrier: %ld/%ld:%ld ",

		n_barrier_successes,

		n_barrier_attempts,

		n_rcu_torture_barrier_error);

	pr_cont("cbflood: %ld\n", atomic_long_read(&n_cbfloods));



	pr_alert("%s%s ", torture_type, TORTURE_FLAG);

	if (atomic_read(&n_rcu_torture_mberror) != 0 ||
@@ -1432,6 +1496,8 @@ rcu_torture_cleanup(void) 


	torture_stop_kthread(rcu_torture_stats, stats_task);

	torture_stop_kthread(rcu_torture_fqs, fqs_task);

	for (i = 0; i < ncbflooders; i++)

		torture_stop_kthread(rcu_torture_cbflood, cbflood_task[i]);

	if ((test_boost == 1 && cur_ops->can_boost) ||

	    test_boost == 2) {

		unregister_cpu_notifier(&rcutorture_cpu_nb);
@@ -1678,6 +1744,24 @@ rcu_torture_init(void) 
		goto unwind;

	if (object_debug)

		rcu_test_debug_objects();

	if (cbflood_n_burst > 0) {

		/* Create the cbflood threads */

		ncbflooders = (num_online_cpus() + 3) / 4;

		cbflood_task = kcalloc(ncbflooders, sizeof(*cbflood_task),

				       GFP_KERNEL);

		if (!cbflood_task) {

			VERBOSE_TOROUT_ERRSTRING("out of memory");

			firsterr = -ENOMEM;

			goto unwind;

		}

		for (i = 0; i < ncbflooders; i++) {

			firsterr = torture_create_kthread(rcu_torture_cbflood,

							  NULL,

							  cbflood_task[i]);

			if (firsterr)

				goto unwind;

		}

	}

	rcutorture_record_test_transition();

	torture_init_end();

	return 0;

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