staging: lustre: ptlrpc: use workqueue for pinger

lustre has a "Pinger" kthread which periodically pings peers
to ensure all hosts are functioning.

This can more easily be done using a work queue.

As maintaining contact with other peers is import for
keeping the filesystem running, and as the filesystem might
be involved in freeing memory, it is safest to have a
separate WQ_MEM_RECLAIM workqueue.

The SVC_EVENT functionality to wake up the thread can be
replaced with mod_delayed_work().

Also use round_jiffies_up_relative() rather than setting a
minimum of 1 second delay.  The PING_INTERVAL is measured in
seconds so this meets the need is allow the workqueue to
keep wakeups synchronized.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ptlrpc/pinger.c

@@ -217,21 +217,18 @@ static void ptlrpc_pinger_process_import(struct obd_import *imp,
 	}
 }
 
-static int ptlrpc_pinger_main(void *arg)
-{
-	struct ptlrpc_thread *thread = arg;
-
-	/* Record that the thread is running */
-	thread_set_flags(thread, SVC_RUNNING);
-	wake_up(&thread->t_ctl_waitq);
+static struct workqueue_struct *pinger_wq;
+static void ptlrpc_pinger_main(struct work_struct *ws);
+static DECLARE_DELAYED_WORK(ping_work, ptlrpc_pinger_main);
 
-	/* And now, loop forever, pinging as needed. */
-	while (1) {
-		unsigned long this_ping = cfs_time_current();
-		long time_to_next_wake;
-		struct timeout_item *item;
-		struct obd_import *imp;
+static void ptlrpc_pinger_main(struct work_struct *ws)
+{
+	unsigned long this_ping = cfs_time_current();
+	long time_to_next_wake;
+	struct timeout_item *item;
+	struct obd_import *imp;
 
+	do {
 		mutex_lock(&pinger_mutex);
 		list_for_each_entry(item, &timeout_list, ti_chain) {
 			item->ti_cb(item, item->ti_cb_data);
@@ -260,50 +257,24 @@ static int ptlrpc_pinger_main(void *arg)
 		       time_to_next_wake,
 		       cfs_time_add(this_ping,
 				    PING_INTERVAL * HZ));
-		if (time_to_next_wake > 0) {
-			wait_event_idle_timeout(thread->t_ctl_waitq,
-						thread_is_stopping(thread) ||
-						thread_is_event(thread),
-						max_t(long, time_to_next_wake, HZ));
-			if (thread_test_and_clear_flags(thread, SVC_STOPPING))
-				break;
-			/* woken after adding import to reset timer */
-			thread_test_and_clear_flags(thread, SVC_EVENT);
-		}
-	}
+	} while (time_to_next_wake <= 0);
 
-	thread_set_flags(thread, SVC_STOPPED);
-	wake_up(&thread->t_ctl_waitq);
-
-	CDEBUG(D_NET, "pinger thread exiting, process %d\n", current_pid());
-	return 0;
+	queue_delayed_work(pinger_wq, &ping_work,
+			   round_jiffies_up_relative(time_to_next_wake));
 }
 
-static struct ptlrpc_thread pinger_thread;
-
 int ptlrpc_start_pinger(void)
 {
-	struct task_struct *task;
-	int rc;
-
-	if (!thread_is_init(&pinger_thread) &&
-	    !thread_is_stopped(&pinger_thread))
+	if (pinger_wq)
 		return -EALREADY;
 
-	init_waitqueue_head(&pinger_thread.t_ctl_waitq);
-
-	strcpy(pinger_thread.t_name, "ll_ping");
-
-	task = kthread_run(ptlrpc_pinger_main, &pinger_thread,
-			   pinger_thread.t_name);
-	if (IS_ERR(task)) {
-		rc = PTR_ERR(task);
-		CERROR("cannot start pinger thread: rc = %d\n", rc);
-		return rc;
+	pinger_wq = alloc_workqueue("ptlrpc_pinger", WQ_MEM_RECLAIM, 1);
+	if (!pinger_wq) {
+		CERROR("cannot start pinger workqueue\n");
+		return -ENOMEM;
 	}
-	wait_event_idle(pinger_thread.t_ctl_waitq,
-			thread_is_running(&pinger_thread));
 
+	queue_delayed_work(pinger_wq, &ping_work, 0);
 	return 0;
 }
 
@@ -313,16 +284,13 @@ int ptlrpc_stop_pinger(void)
 {
 	int rc = 0;
 
-	if (thread_is_init(&pinger_thread) ||
-	    thread_is_stopped(&pinger_thread))
+	if (!pinger_wq)
 		return -EALREADY;
 
 	ptlrpc_pinger_remove_timeouts();
-	thread_set_flags(&pinger_thread, SVC_STOPPING);
-	wake_up(&pinger_thread.t_ctl_waitq);
-
-	wait_event_idle(pinger_thread.t_ctl_waitq,
-			thread_is_stopped(&pinger_thread));
+	cancel_delayed_work_sync(&ping_work);
+	destroy_workqueue(pinger_wq);
+	pinger_wq = NULL;
 
 	return rc;
 }
@@ -505,6 +473,5 @@ static int ptlrpc_pinger_remove_timeouts(void)
 
 void ptlrpc_pinger_wake_up(void)
 {
-	thread_add_flags(&pinger_thread, SVC_EVENT);
-	wake_up(&pinger_thread.t_ctl_waitq);
+	mod_delayed_work(pinger_wq, &ping_work, 0);
 }