rcutorture: Enable multiple concurrent callback-flood kthreads

This commit converts the rcutorture.fwd_progress module parameter from
bool to int, so that it specifies the number of callback-flood kthreads.
Values less than zero specify one kthread per CPU, however, the number of
kthreads executing concurrently is limited to the number of online CPUs.
This commit also reverse the order of the need-resched and callback-flood
operations to cause the callback flooding to happen more nearly at the
same time.

Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -4603,8 +4603,12 @@
 			in seconds.
 
 	rcutorture.fwd_progress= [KNL]
-			Enable RCU grace-period forward-progress testing
+			Specifies the number of kthreads to be used
+			for  RCU grace-period forward-progress testing
 			for the types of RCU supporting this notion.
+			Defaults to 1 kthread, values less than zero or
+			greater than the number of CPUs cause the number
+			of CPUs to be used.
 
 	rcutorture.fwd_progress_div= [KNL]
 			Specify the fraction of a CPU-stall-warning

kernel/rcu/rcutorture.c

@@ -79,7 +79,7 @@ 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)");
 torture_param(int, fqs_stutter, 3, "Wait time between fqs bursts (s)");
-torture_param(bool, fwd_progress, 1, "Test grace-period forward progress");
+torture_param(int, fwd_progress, 1, "Test grace-period forward progress");
 torture_param(int, fwd_progress_div, 4, "Fraction of CPU stall to wait");
 torture_param(int, fwd_progress_holdoff, 60,
 	      "Time between forward-progress tests (s)");
@@ -146,7 +146,7 @@ static struct task_struct *stats_task;
 static struct task_struct *fqs_task;
 static struct task_struct *boost_tasks[NR_CPUS];
 static struct task_struct *stall_task;
-static struct task_struct *fwd_prog_task;
+static struct task_struct **fwd_prog_tasks;
 static struct task_struct **barrier_cbs_tasks;
 static struct task_struct *barrier_task;
 static struct task_struct *read_exit_task;
@@ -2161,10 +2161,12 @@ struct rcu_fwd {
 	unsigned long rcu_fwd_startat;
 	struct rcu_launder_hist n_launders_hist[N_LAUNDERS_HIST];
 	unsigned long rcu_launder_gp_seq_start;
+	int rcu_fwd_id;
 };
 
 static DEFINE_MUTEX(rcu_fwd_mutex);
 static struct rcu_fwd *rcu_fwds;
+static unsigned long rcu_fwd_seq;
 static bool rcu_fwd_emergency_stop;
 
 static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
@@ -2177,8 +2179,9 @@ static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
 	for (i = ARRAY_SIZE(rfp->n_launders_hist) - 1; i > 0; i--)
 		if (rfp->n_launders_hist[i].n_launders > 0)
 			break;
-	pr_alert("%s: Callback-invocation histogram (duration %lu jiffies):",
-		 __func__, jiffies - rfp->rcu_fwd_startat);
+	mutex_lock(&rcu_fwd_mutex); // Serialize histograms.
+	pr_alert("%s: Callback-invocation histogram %d (duration %lu jiffies):",
+		 __func__, rfp->rcu_fwd_id, jiffies - rfp->rcu_fwd_startat);
 	gps_old = rfp->rcu_launder_gp_seq_start;
 	for (j = 0; j <= i; j++) {
 		gps = rfp->n_launders_hist[j].launder_gp_seq;
@@ -2189,6 +2192,7 @@ static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
 		gps_old = gps;
 	}
 	pr_cont("\n");
+	mutex_unlock(&rcu_fwd_mutex);
 }
 
 /* Callback function for continuous-flood RCU callbacks. */
@@ -2314,7 +2318,8 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp,
 		cver = READ_ONCE(rcu_torture_current_version) - cver;
 		gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps);
 		WARN_ON(!cver && gps < 2);
-		pr_alert("%s: Duration %ld cver %ld gps %ld\n", __func__, dur, cver, gps);
+		pr_alert("%s: %d Duration %ld cver %ld gps %ld\n", __func__,
+			 rfp->rcu_fwd_id, dur, cver, gps);
 	}
 	if (selfpropcb) {
 		WRITE_ONCE(fcs.stop, 1);
@@ -2432,6 +2437,8 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
 static int rcutorture_oom_notify(struct notifier_block *self,
 				 unsigned long notused, void *nfreed)
 {
+	int i;
+	long ncbs;
 	struct rcu_fwd *rfp;
 
 	mutex_lock(&rcu_fwd_mutex);
@@ -2442,18 +2449,26 @@ static int rcutorture_oom_notify(struct notifier_block *self,
 	}
 	WARN(1, "%s invoked upon OOM during forward-progress testing.\n",
 	     __func__);
-	rcu_torture_fwd_cb_hist(rfp);
-	rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rfp->rcu_fwd_startat)) / 2);
+	for (i = 0; i < fwd_progress; i++) {
+		rcu_torture_fwd_cb_hist(&rfp[i]);
+		rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rfp[i].rcu_fwd_startat)) / 2);
+	}
 	WRITE_ONCE(rcu_fwd_emergency_stop, true);
 	smp_mb(); /* Emergency stop before free and wait to avoid hangs. */
-	pr_info("%s: Freed %lu RCU callbacks.\n",
-		__func__, rcu_torture_fwd_prog_cbfree(rfp));
+	ncbs = 0;
+	for (i = 0; i < fwd_progress; i++)
+		ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]);
+	pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs);
 	rcu_barrier();
-	pr_info("%s: Freed %lu RCU callbacks.\n",
-		__func__, rcu_torture_fwd_prog_cbfree(rfp));
+	ncbs = 0;
+	for (i = 0; i < fwd_progress; i++)
+		ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]);
+	pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs);
 	rcu_barrier();
-	pr_info("%s: Freed %lu RCU callbacks.\n",
-		__func__, rcu_torture_fwd_prog_cbfree(rfp));
+	ncbs = 0;
+	for (i = 0; i < fwd_progress; i++)
+		ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]);
+	pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs);
 	smp_mb(); /* Frees before return to avoid redoing OOM. */
 	(*(unsigned long *)nfreed)++; /* Forward progress CBs freed! */
 	pr_info("%s returning after OOM processing.\n", __func__);
@@ -2469,6 +2484,7 @@ static struct notifier_block rcutorture_oom_nb = {
 static int rcu_torture_fwd_prog(void *args)
 {
 	int oldnice = task_nice(current);
+	unsigned long oldseq = READ_ONCE(rcu_fwd_seq);
 	struct rcu_fwd *rfp = args;
 	int tested = 0;
 	int tested_tries = 0;
@@ -2478,21 +2494,31 @@ static int rcu_torture_fwd_prog(void *args)
 	if (!IS_ENABLED(CONFIG_SMP) || !IS_ENABLED(CONFIG_RCU_BOOST))
 		set_user_nice(current, MAX_NICE);
 	do {
+		if (!rfp->rcu_fwd_id) {
 			schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
 			WRITE_ONCE(rcu_fwd_emergency_stop, false);
+			WRITE_ONCE(rcu_fwd_seq, rcu_fwd_seq + 1);
+		} else {
+			while (READ_ONCE(rcu_fwd_seq) == oldseq)
+				schedule_timeout_interruptible(1);
+			oldseq = READ_ONCE(rcu_fwd_seq);
+		}
+		pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id);
+		if (rcu_inkernel_boot_has_ended() && torture_num_online_cpus() > rfp->rcu_fwd_id)
+			rcu_torture_fwd_prog_cr(rfp);
 		if (!IS_ENABLED(CONFIG_TINY_RCU) ||
-		    rcu_inkernel_boot_has_ended())
+		    (rcu_inkernel_boot_has_ended() && torture_num_online_cpus() > rfp->rcu_fwd_id))
 			rcu_torture_fwd_prog_nr(rfp, &tested, &tested_tries);
-		if (rcu_inkernel_boot_has_ended())
-			rcu_torture_fwd_prog_cr(rfp);
 
 		/* Avoid slow periods, better to test when busy. */
 		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. */
+	if (!rfp->rcu_fwd_id) {
 		WARN_ON(!tested && tested_tries >= 5);
 		pr_alert("%s: tested %d tested_tries %d\n", __func__, tested, tested_tries);
+	}
 	torture_kthread_stopping("rcu_torture_fwd_prog");
 	return 0;
 }
@@ -2500,17 +2526,27 @@ static int rcu_torture_fwd_prog(void *args)
 /* If forward-progress checking is requested and feasible, spawn the thread. */
 static int __init rcu_torture_fwd_prog_init(void)
 {
+	int i;
+	int ret = 0;
 	struct rcu_fwd *rfp;
 
 	if (!fwd_progress)
 		return 0; /* Not requested, so don't do it. */
+	if (fwd_progress >= nr_cpu_ids) {
+		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Limiting fwd_progress to # CPUs.\n");
+		fwd_progress = nr_cpu_ids;
+	} else if (fwd_progress < 0) {
+		fwd_progress = nr_cpu_ids;
+	}
 	if ((!cur_ops->sync && !cur_ops->call) ||
 	    !cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || cur_ops == &rcu_busted_ops) {
 		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
+		fwd_progress = 0;
 		return 0;
 	}
 	if (stall_cpu > 0) {
 		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, conflicts with CPU-stall testing");
+		fwd_progress = 0;
 		if (IS_MODULE(CONFIG_RCU_TORTURE_TEST))
 			return -EINVAL; /* In module, can fail back to user. */
 		WARN_ON(1); /* Make sure rcutorture notices conflict. */
@@ -2520,29 +2556,51 @@ static int __init rcu_torture_fwd_prog_init(void)
 		fwd_progress_holdoff = 1;
 	if (fwd_progress_div <= 0)
 		fwd_progress_div = 4;
-	rfp = kzalloc(sizeof(*rfp), GFP_KERNEL);
-	if (!rfp)
+	rfp = kcalloc(fwd_progress, sizeof(*rfp), GFP_KERNEL);
+	fwd_prog_tasks = kcalloc(fwd_progress, sizeof(*fwd_prog_tasks), GFP_KERNEL);
+	if (!rfp || !fwd_prog_tasks) {
+		kfree(rfp);
+		kfree(fwd_prog_tasks);
+		fwd_prog_tasks = NULL;
+		fwd_progress = 0;
 		return -ENOMEM;
-	spin_lock_init(&rfp->rcu_fwd_lock);
-	rfp->rcu_fwd_cb_tail = &rfp->rcu_fwd_cb_head;
+	}
+	for (i = 0; i < fwd_progress; i++) {
+		spin_lock_init(&rfp[i].rcu_fwd_lock);
+		rfp[i].rcu_fwd_cb_tail = &rfp[i].rcu_fwd_cb_head;
+		rfp[i].rcu_fwd_id = i;
+	}
 	mutex_lock(&rcu_fwd_mutex);
 	rcu_fwds = rfp;
 	mutex_unlock(&rcu_fwd_mutex);
 	register_oom_notifier(&rcutorture_oom_nb);
-	return torture_create_kthread(rcu_torture_fwd_prog, rfp, fwd_prog_task);
+	for (i = 0; i < fwd_progress; i++) {
+		ret = torture_create_kthread(rcu_torture_fwd_prog, &rcu_fwds[i], fwd_prog_tasks[i]);
+		if (ret) {
+			fwd_progress = i;
+			return ret;
+		}
+	}
+	return 0;
 }
 
 static void rcu_torture_fwd_prog_cleanup(void)
 {
+	int i;
 	struct rcu_fwd *rfp;
 
-	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
-	rfp = rcu_fwds;
+	if (!rcu_fwds || !fwd_prog_tasks)
+		return;
+	for (i = 0; i < fwd_progress; i++)
+		torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_tasks[i]);
+	unregister_oom_notifier(&rcutorture_oom_nb);
 	mutex_lock(&rcu_fwd_mutex);
+	rfp = rcu_fwds;
 	rcu_fwds = NULL;
 	mutex_unlock(&rcu_fwd_mutex);
-	unregister_oom_notifier(&rcutorture_oom_nb);
 	kfree(rfp);
+	kfree(fwd_prog_tasks);
+	fwd_prog_tasks = NULL;
 }
 
 /* Callback function for RCU barrier testing. */