Commit ab1b7880 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcutorture: Make stutter_wait() caller restore priority 



Currently, stutter_wait() will happily spin waiting for the stutter
interval to end even if the caller is running at a real-time priority
level.  This could starve normal-priority tasks for no good reason.  This
commit therefore drops the calling task's priority to SCHED_OTHER MAX_NICE
if stutter_wait() needs to wait.  But when it waits, stutter_wait()
returns true, which allows the caller to restore the priority if needed.
Callers that were already running at SCHED_OTHER MAX_NICE obviously
do not need any changes, but this commit also restores priority for
higher-priority callers.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent c1e06287

kernel/rcu/rcutorture.c

+18 −6
Original line number Diff line number Diff line
@@ -912,7 +912,8 @@ static int rcu_torture_boost(void *arg) 
		oldstarttime = boost_starttime;

		while (time_before(jiffies, oldstarttime)) {

			schedule_timeout_interruptible(oldstarttime - jiffies);

			stutter_wait("rcu_torture_boost");

			if (stutter_wait("rcu_torture_boost"))

				sched_set_fifo_low(current);

			if (torture_must_stop())

				goto checkwait;

		}
@@ -932,7 +933,8 @@ static int rcu_torture_boost(void *arg) 
								 jiffies);

				call_rcu_time = jiffies;

			}

			stutter_wait("rcu_torture_boost");

			if (stutter_wait("rcu_torture_boost"))

				sched_set_fifo_low(current);

			if (torture_must_stop())

				goto checkwait;

		}
@@ -964,7 +966,8 @@ static int rcu_torture_boost(void *arg) 
		}



		/* Go do the stutter. */

checkwait:	stutter_wait("rcu_torture_boost");

checkwait:	if (stutter_wait("rcu_torture_boost"))

			sched_set_fifo_low(current);

	} while (!torture_must_stop());



	/* Clean up and exit. */
@@ -987,6 +990,7 @@ rcu_torture_fqs(void *arg) 
{

	unsigned long fqs_resume_time;

	int fqs_burst_remaining;

	int oldnice = task_nice(current);



	VERBOSE_TOROUT_STRING("rcu_torture_fqs task started");

	do {
@@ -1002,7 +1006,8 @@ rcu_torture_fqs(void *arg) 
			udelay(fqs_holdoff);

			fqs_burst_remaining -= fqs_holdoff;

		}

		stutter_wait("rcu_torture_fqs");

		if (stutter_wait("rcu_torture_fqs"))

			sched_set_normal(current, oldnice);

	} while (!torture_must_stop());

	torture_kthread_stopping("rcu_torture_fqs");

	return 0;
@@ -1022,9 +1027,11 @@ rcu_torture_writer(void *arg) 
	bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;

	bool gp_sync1 = gp_sync;

	int i;

	int oldnice = task_nice(current);

	struct rcu_torture *rp;

	struct rcu_torture *old_rp;

	static DEFINE_TORTURE_RANDOM(rand);

	bool stutter_waited;

	int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC,

			   RTWS_COND_GET, RTWS_SYNC };

	int nsynctypes = 0;
@@ -1143,7 +1150,8 @@ rcu_torture_writer(void *arg) 
				       !rcu_gp_is_normal();

		}

		rcu_torture_writer_state = RTWS_STUTTER;

		if (stutter_wait("rcu_torture_writer") &&

		stutter_waited = stutter_wait("rcu_torture_writer");

		if (stutter_waited &&

		    !READ_ONCE(rcu_fwd_cb_nodelay) &&

		    !cur_ops->slow_gps &&

		    !torture_must_stop() &&
@@ -1155,6 +1163,8 @@ rcu_torture_writer(void *arg) 
					rcu_ftrace_dump(DUMP_ALL);

					WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);

				}

		if (stutter_waited)

			sched_set_normal(current, oldnice);

	} while (!torture_must_stop());

	rcu_torture_current = NULL;  // Let stats task know that we are done.

	/* Reset expediting back to unexpedited. */
@@ -2103,6 +2113,7 @@ static struct notifier_block rcutorture_oom_nb = { 
/* Carry out grace-period forward-progress testing. */

static int rcu_torture_fwd_prog(void *args)

{

	int oldnice = task_nice(current);

	struct rcu_fwd *rfp = args;

	int tested = 0;

	int tested_tries = 0;
@@ -2121,7 +2132,8 @@ static int rcu_torture_fwd_prog(void *args) 
			rcu_torture_fwd_prog_cr(rfp);



		/* Avoid slow periods, better to test when busy. */

		stutter_wait("rcu_torture_fwd_prog");

		if (stutter_wait("rcu_torture_fwd_prog"))

			sched_set_normal(current, oldnice);

	} while (!torture_must_stop());

	/* Short runs might not contain a valid forward-progress attempt. */

	WARN_ON(!tested && tested_tries >= 5);

kernel/torture.c

+4 −5
Original line number Diff line number Diff line
@@ -604,19 +604,19 @@ bool stutter_wait(const char *title) 
{

	ktime_t delay;

	unsigned int i = 0;

	int oldnice;

	bool ret = false;

	int spt;



	cond_resched_tasks_rcu_qs();

	spt = READ_ONCE(stutter_pause_test);

	for (; spt; spt = READ_ONCE(stutter_pause_test)) {

		if (!ret) {

			sched_set_normal(current, MAX_NICE);

			ret = true;

		}

		if (spt == 1) {

			schedule_timeout_interruptible(1);

		} else if (spt == 2) {

			oldnice = task_nice(current);

			set_user_nice(current, MAX_NICE);

			while (READ_ONCE(stutter_pause_test)) {

				if (!(i++ & 0xffff)) {

					set_current_state(TASK_INTERRUPTIBLE);
@@ -625,7 +625,6 @@ bool stutter_wait(const char *title) 
				}

				cond_resched();

			}

			set_user_nice(current, oldnice);

		} else {

			schedule_timeout_interruptible(round_jiffies_relative(HZ));

		}