rcutorture: Remove cbflood facility

Now that the forward-progress code does a full-bore continuous callback
flood lasting multiple seconds, there is little point in also posting a
mere 60,000 callbacks every second or so.  This commit therefore removes
the old cbflood testing.  Over time, it may be desirable to concurrently
do full-bore continuous callback floods on all CPUs simultaneously, but
one dragon at a time.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -3743,24 +3743,6 @@
 			in microseconds.  The default of zero says
 			no holdoff.
 
-	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
 			in microseconds.

kernel/rcu/rcutorture.c

@@ -80,13 +80,6 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and Josh Triplett <josh@jos
 					/* Must be power of two minus one. */
 #define RCUTORTURE_RDR_MAX_SEGS (RCUTORTURE_RDR_MAX_LOOPS + 3)
 
-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, extendables, RCUTORTURE_MAX_EXTEND,
 	      "Extend readers by disabling bh (1), irqs (2), or preempt (4)");
 torture_param(int, fqs_duration, 0,
@@ -138,12 +131,10 @@ module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)");
 
 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;
@@ -181,7 +172,6 @@ static long n_rcu_torture_boosts;
 static atomic_long_t n_rcu_torture_timers;
 static long n_barrier_attempts;
 static long n_barrier_successes; /* did rcu_barrier test succeed? */
-static atomic_long_t n_cbfloods;
 static struct list_head rcu_torture_removed;
 
 static int rcu_torture_writer_state;
@@ -873,59 +863,6 @@ 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(array3_size(cbflood_n_burst,
-					  cbflood_n_per_burst,
-					  sizeof(*rhp)));
-		err = !rhp;
-	}
-	if (err) {
-		VERBOSE_TOROUT_STRING("rcu_torture_cbflood disabled: Bad args or OOM");
-		goto wait_for_stop;
-	}
-	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());
-	vfree(rhp);
-wait_for_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
@@ -1460,11 +1397,10 @@ rcu_torture_stats_print(void)
 		n_rcu_torture_boosts,
 		atomic_long_read(&n_rcu_torture_timers));
 	torture_onoff_stats();
-	pr_cont("barrier: %ld/%ld:%ld ",
+	pr_cont("barrier: %ld/%ld:%ld\n",
 		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 ||
@@ -2093,8 +2029,6 @@ rcu_torture_cleanup(void)
 		 cur_ops->name, gp_seq, flags);
 	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 (rcu_torture_can_boost())
 		cpuhp_remove_state(rcutor_hp);
 
@@ -2377,24 +2311,6 @@ 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;
-		}
-	}
 	torture_init_end();
 	return 0;