Commit 55b2dcf5 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Allow rcutorture to starve grace-period kthread 



This commit provides an rcutorture.stall_gp_kthread module parameter
to allow rcutorture to starve the grace-period kthread.  This allows
testing the code that detects such starvation.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent df591684

Documentation/admin-guide/kernel-parameters.txt

+7 −0
Original line number Diff line number Diff line
@@ -4221,6 +4221,13 @@ 
	rcutorture.stall_cpu_irqsoff= [KNL]

			Disable interrupts while stalling if set.



	rcutorture.stall_gp_kthread= [KNL]

			Duration (s) of forced sleep within RCU

			grace-period kthread to test RCU CPU stall

			warnings, zero to disable.  If both stall_cpu

			and stall_gp_kthread are specified, the

			kthread is starved first, then the CPU.



	rcutorture.stat_interval= [KNL]

			Time (s) between statistics printk()s.

kernel/rcu/rcu.h

+2 −0
Original line number Diff line number Diff line
@@ -454,6 +454,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename, 
			       unsigned long secs,

			       unsigned long c_old,

			       unsigned long c);

void rcu_gp_set_torture_wait(int duration);

#else

static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,

					  int *flags, unsigned long *gp_seq)
@@ -471,6 +472,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename, 
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \

	do { } while (0)

#endif

static inline void rcu_gp_set_torture_wait(int duration) { }

#endif



#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)

kernel/rcu/rcutorture.c

+15 −3
Original line number Diff line number Diff line
@@ -115,6 +115,8 @@ torture_param(int, stall_cpu_holdoff, 10, 
	     "Time to wait before starting stall (s).");

torture_param(int, stall_cpu_irqsoff, 0, "Disable interrupts while stalling.");

torture_param(int, stall_cpu_block, 0, "Sleep while stalling.");

torture_param(int, stall_gp_kthread, 0,

	      "Grace-period kthread stall duration (s).");

torture_param(int, stat_interval, 60,

	     "Number of seconds between stats printk()s");

torture_param(int, stutter, 5, "Number of seconds to run/halt test");
@@ -1623,7 +1625,17 @@ static int rcu_torture_stall(void *args) 
		schedule_timeout_interruptible(stall_cpu_holdoff * HZ);

		VERBOSE_TOROUT_STRING("rcu_torture_stall end holdoff");

	}

	if (!kthread_should_stop()) {

	if (!kthread_should_stop() && stall_gp_kthread > 0) {

		VERBOSE_TOROUT_STRING("rcu_torture_stall begin GP stall");

		rcu_gp_set_torture_wait(stall_gp_kthread * HZ);

		for (idx = 0; idx < stall_gp_kthread + 2; idx++) {

			if (kthread_should_stop())

				break;

			schedule_timeout_uninterruptible(HZ);

		}

	}

	if (!kthread_should_stop() && stall_cpu > 0) {

		VERBOSE_TOROUT_STRING("rcu_torture_stall begin CPU stall");

		stop_at = ktime_get_seconds() + stall_cpu;

		/* RCU CPU stall is expected behavior in following code. */

		idx = cur_ops->readlock();
@@ -1642,8 +1654,8 @@ static int rcu_torture_stall(void *args) 
		else if (!stall_cpu_block)

			preempt_enable();

		cur_ops->readunlock(idx);

		pr_alert("rcu_torture_stall end.\n");

	}

	pr_alert("rcu_torture_stall end.\n");

	torture_shutdown_absorb("rcu_torture_stall");

	while (!kthread_should_stop())

		schedule_timeout_interruptible(10 * HZ);
@@ -1653,7 +1665,7 @@ static int rcu_torture_stall(void *args) 
/* Spawn CPU-stall kthread, if stall_cpu specified. */

static int __init rcu_torture_stall_init(void)

{

	if (stall_cpu <= 0)

	if (stall_cpu <= 0 && stall_gp_kthread <= 0)

		return 0;

	return torture_create_kthread(rcu_torture_stall, NULL, stall_task);

}

kernel/rcu/tree.c

+27 −0
Original line number Diff line number Diff line
@@ -1486,6 +1486,31 @@ static void rcu_gp_slow(int delay) 
		schedule_timeout_uninterruptible(delay);

}



static unsigned long sleep_duration;



/* Allow rcutorture to stall the grace-period kthread. */

void rcu_gp_set_torture_wait(int duration)

{

	if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)

		WRITE_ONCE(sleep_duration, duration);

}

EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);



/* Actually implement the aforementioned wait. */

static void rcu_gp_torture_wait(void)

{

	unsigned long duration;



	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))

		return;

	duration = xchg(&sleep_duration, 0UL);

	if (duration > 0) {

		pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);

		schedule_timeout_uninterruptible(duration);

		pr_alert("%s: Wait complete\n", __func__);

	}

}



/*

 * Initialize a new grace period.  Return false if no grace period required.

 */
@@ -1686,6 +1711,7 @@ static void rcu_gp_fqs_loop(void) 
		rcu_state.gp_state = RCU_GP_WAIT_FQS;

		ret = swait_event_idle_timeout_exclusive(

				rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);

		rcu_gp_torture_wait();

		rcu_state.gp_state = RCU_GP_DOING_FQS;

		/* Locking provides needed memory barriers. */

		/* If grace period done, leave loop. */
@@ -1834,6 +1860,7 @@ static int __noreturn rcu_gp_kthread(void *unused) 
			swait_event_idle_exclusive(rcu_state.gp_wq,

					 READ_ONCE(rcu_state.gp_flags) &

					 RCU_GP_FLAG_INIT);

			rcu_gp_torture_wait();

			rcu_state.gp_state = RCU_GP_DONE_GPS;

			/* Locking provides needed memory barrier. */

			if (rcu_gp_init())