rcu: fix rcutorture behavior during reboot

Impact: fix very rare reboot hang

Because rcutorture ignored all signals, it does not terminate in
response to the signals sent at shutdown time.  This can cause strange
failures due to its continuing to make use of kernel function too late
in the shutdown sequence.  This patch therefore adds a shutdown notifier
to rcutorture, causing it to shut down in response to a reboot or an
orderly shutdown.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/rcutorture.c

@@ -39,6 +39,7 @@
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
+#include <linux/reboot.h>
 #include <linux/freezer.h>
 #include <linux/cpu.h>
 #include <linux/delay.h>
@@ -108,7 +109,6 @@ struct rcu_torture {
 	int rtort_mbtest;
 };
 
-static int fullstop = 0;	/* stop generating callbacks at test end. */
 static LIST_HEAD(rcu_torture_freelist);
 static struct rcu_torture *rcu_torture_current = NULL;
 static long rcu_torture_current_version = 0;
@@ -136,6 +136,30 @@ static int stutter_pause_test = 0;
 #endif
 int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT;
 
+#define FULLSTOP_SIGNALED 1	/* Bail due to signal. */
+#define FULLSTOP_CLEANUP  2	/* Orderly shutdown. */
+static int fullstop;		/* stop generating callbacks at test end. */
+DEFINE_MUTEX(fullstop_mutex);	/* protect fullstop transitions and */
+				/*  spawning of kthreads. */
+
+/*
+ * Detect and respond to a signal-based shutdown.
+ */
+static int
+rcutorture_shutdown_notify(struct notifier_block *unused1,
+			   unsigned long unused2, void *unused3)
+{
+	if (fullstop)
+		return NOTIFY_DONE;
+	if (signal_pending(current)) {
+		mutex_lock(&fullstop_mutex);
+		if (!ACCESS_ONCE(fullstop))
+			fullstop = FULLSTOP_SIGNALED;
+		mutex_unlock(&fullstop_mutex);
+	}
+	return NOTIFY_DONE;
+}
+
 /*
  * Allocate an element from the rcu_tortures pool.
  */
@@ -199,11 +223,12 @@ rcu_random(struct rcu_random_state *rrsp)
 static void
 rcu_stutter_wait(void)
 {
-	while (stutter_pause_test || !rcutorture_runnable)
+	while ((stutter_pause_test || !rcutorture_runnable) && !fullstop) {
 		if (rcutorture_runnable)
 			schedule_timeout_interruptible(1);
 		else
 			schedule_timeout_interruptible(round_jiffies_relative(HZ));
+	}
 }
 
 /*
@@ -599,7 +624,7 @@ rcu_torture_writer(void *arg)
 		rcu_stutter_wait();
 	} while (!kthread_should_stop() && !fullstop);
 	VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
-	while (!kthread_should_stop())
+	while (!kthread_should_stop() && fullstop != FULLSTOP_SIGNALED)
 		schedule_timeout_uninterruptible(1);
 	return 0;
 }
@@ -624,7 +649,7 @@ rcu_torture_fakewriter(void *arg)
 	} while (!kthread_should_stop() && !fullstop);
 
 	VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task stopping");
-	while (!kthread_should_stop())
+	while (!kthread_should_stop() && fullstop != FULLSTOP_SIGNALED)
 		schedule_timeout_uninterruptible(1);
 	return 0;
 }
@@ -734,7 +759,7 @@ rcu_torture_reader(void *arg)
 	VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
 	if (irqreader && cur_ops->irqcapable)
 		del_timer_sync(&t);
-	while (!kthread_should_stop())
+	while (!kthread_should_stop() && fullstop != FULLSTOP_SIGNALED)
 		schedule_timeout_uninterruptible(1);
 	return 0;
 }
@@ -831,7 +856,7 @@ rcu_torture_stats(void *arg)
 	do {
 		schedule_timeout_interruptible(stat_interval * HZ);
 		rcu_torture_stats_print();
-	} while (!kthread_should_stop());
+	} while (!kthread_should_stop() && !fullstop);
 	VERBOSE_PRINTK_STRING("rcu_torture_stats task stopping");
 	return 0;
 }
@@ -899,7 +924,7 @@ rcu_torture_shuffle(void *arg)
 	do {
 		schedule_timeout_interruptible(shuffle_interval * HZ);
 		rcu_torture_shuffle_tasks();
-	} while (!kthread_should_stop());
+	} while (!kthread_should_stop() && !fullstop);
 	VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
 	return 0;
 }
@@ -914,10 +939,10 @@ rcu_torture_stutter(void *arg)
 	do {
 		schedule_timeout_interruptible(stutter * HZ);
 		stutter_pause_test = 1;
-		if (!kthread_should_stop())
+		if (!kthread_should_stop() && !fullstop)
 			schedule_timeout_interruptible(stutter * HZ);
 		stutter_pause_test = 0;
-	} while (!kthread_should_stop());
+	} while (!kthread_should_stop() && !fullstop);
 	VERBOSE_PRINTK_STRING("rcu_torture_stutter task stopping");
 	return 0;
 }
@@ -934,12 +959,27 @@ rcu_torture_print_module_parms(char *tag)
 		stutter, irqreader);
 }
 
+static struct notifier_block rcutorture_nb = {
+	.notifier_call = rcutorture_shutdown_notify,
+};
+
 static void
 rcu_torture_cleanup(void)
 {
 	int i;
 
-	fullstop = 1;
+	mutex_lock(&fullstop_mutex);
+	if (!fullstop) {
+		/* If being signaled, let it happen, then exit. */
+		mutex_unlock(&fullstop_mutex);
+		schedule_timeout_interruptible(10 * HZ);
+		if (cur_ops->cb_barrier != NULL)
+			cur_ops->cb_barrier();
+		return;
+	}
+	fullstop = FULLSTOP_CLEANUP;
+	mutex_unlock(&fullstop_mutex);
+	unregister_reboot_notifier(&rcutorture_nb);
 	if (stutter_task) {
 		VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
 		kthread_stop(stutter_task);
@@ -1015,6 +1055,8 @@ rcu_torture_init(void)
 		{ &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
 		  &srcu_ops, &sched_ops, &sched_ops_sync, };
 
+	mutex_lock(&fullstop_mutex);
+
 	/* Process args and tell the world that the torturer is on the job. */
 	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
 		cur_ops = torture_ops[i];
@@ -1024,6 +1066,7 @@ rcu_torture_init(void)
 	if (i == ARRAY_SIZE(torture_ops)) {
 		printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"\n",
 		       torture_type);
+		mutex_unlock(&fullstop_mutex);
 		return (-EINVAL);
 	}
 	if (cur_ops->init)
@@ -1146,9 +1189,12 @@ rcu_torture_init(void)
 			goto unwind;
 		}
 	}
+	register_reboot_notifier(&rcutorture_nb);
+	mutex_unlock(&fullstop_mutex);
 	return 0;
 
 unwind:
+	mutex_unlock(&fullstop_mutex);
 	rcu_torture_cleanup();
 	return firsterr;
 }