staging: lustre: ldlm: use delayed_work for pools_recalc

ldlm currenty has a kthread which wakes up every so often
and calls ldlm_pools_recalc().
The thread is started and stopped, but no other external interactions
happen.

This can trivially be replaced by a delayed_work if we have
ldlm_pools_recalc() reschedule the work rather than just report
when to do that.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ldlm/ldlm_pool.c

@@ -784,9 +784,6 @@ static int ldlm_pool_granted(struct ldlm_pool *pl)
 	return atomic_read(&pl->pl_granted);
 }
 
-static struct ptlrpc_thread *ldlm_pools_thread;
-static struct completion ldlm_pools_comp;
-
 /*
  * count locks from all namespaces (if possible). Returns number of
  * cached locks.
@@ -899,8 +896,12 @@ static unsigned long ldlm_pools_cli_scan(struct shrinker *s,
 			       sc->gfp_mask);
 }
 
-static int ldlm_pools_recalc(enum ldlm_side client)
+static void ldlm_pools_recalc(struct work_struct *ws);
+static DECLARE_DELAYED_WORK(ldlm_recalc_pools, ldlm_pools_recalc);
+
+static void ldlm_pools_recalc(struct work_struct *ws)
 {
+	enum ldlm_side client = LDLM_NAMESPACE_CLIENT;
 	struct ldlm_namespace *ns;
 	struct ldlm_namespace *ns_old = NULL;
 	/* seconds of sleep if no active namespaces */
@@ -982,92 +983,19 @@ static int ldlm_pools_recalc(enum ldlm_side client)
 	/* Wake up the blocking threads from time to time. */
 	ldlm_bl_thread_wakeup();
 
-	return time;
-}
-
-static int ldlm_pools_thread_main(void *arg)
-{
-	struct ptlrpc_thread *thread = (struct ptlrpc_thread *)arg;
-	int c_time;
-
-	thread_set_flags(thread, SVC_RUNNING);
-	wake_up(&thread->t_ctl_waitq);
-
-	CDEBUG(D_DLMTRACE, "%s: pool thread starting, process %d\n",
-	       "ldlm_poold", current_pid());
-
-	while (1) {
-		/*
-		 * Recal all pools on this tick.
-		 */
-		c_time = ldlm_pools_recalc(LDLM_NAMESPACE_CLIENT);
-
-		/*
-		 * Wait until the next check time, or until we're
-		 * stopped.
-		 */
-		wait_event_idle_timeout(thread->t_ctl_waitq,
-					thread_is_stopping(thread) ||
-					thread_is_event(thread),
-					c_time * HZ);
-
-		if (thread_test_and_clear_flags(thread, SVC_STOPPING))
-			break;
-		thread_test_and_clear_flags(thread, SVC_EVENT);
-	}
-
-	thread_set_flags(thread, SVC_STOPPED);
-	wake_up(&thread->t_ctl_waitq);
-
-	CDEBUG(D_DLMTRACE, "%s: pool thread exiting, process %d\n",
-	       "ldlm_poold", current_pid());
-
-	complete_and_exit(&ldlm_pools_comp, 0);
+	schedule_delayed_work(&ldlm_recalc_pools, time * HZ);
 }
 
 static int ldlm_pools_thread_start(void)
 {
-	struct task_struct *task;
-
-	if (ldlm_pools_thread)
-		return -EALREADY;
-
-	ldlm_pools_thread = kzalloc(sizeof(*ldlm_pools_thread), GFP_NOFS);
-	if (!ldlm_pools_thread)
-		return -ENOMEM;
-
-	init_completion(&ldlm_pools_comp);
-	init_waitqueue_head(&ldlm_pools_thread->t_ctl_waitq);
+	schedule_delayed_work(&ldlm_recalc_pools, 0);
 
-	task = kthread_run(ldlm_pools_thread_main, ldlm_pools_thread,
-			   "ldlm_poold");
-	if (IS_ERR(task)) {
-		CERROR("Can't start pool thread, error %ld\n", PTR_ERR(task));
-		kfree(ldlm_pools_thread);
-		ldlm_pools_thread = NULL;
-		return PTR_ERR(task);
-	}
-	wait_event_idle(ldlm_pools_thread->t_ctl_waitq,
-			thread_is_running(ldlm_pools_thread));
 	return 0;
 }
 
 static void ldlm_pools_thread_stop(void)
 {
-	if (!ldlm_pools_thread)
-		return;
-
-	thread_set_flags(ldlm_pools_thread, SVC_STOPPING);
-	wake_up(&ldlm_pools_thread->t_ctl_waitq);
-
-	/*
-	 * Make sure that pools thread is finished before freeing @thread.
-	 * This fixes possible race and oops due to accessing freed memory
-	 * in pools thread.
-	 */
-	wait_for_completion(&ldlm_pools_comp);
-	kfree(ldlm_pools_thread);
-	ldlm_pools_thread = NULL;
+	cancel_delayed_work_sync(&ldlm_recalc_pools);
 }
 
 static struct shrinker ldlm_pools_cli_shrinker = {
@@ -1081,20 +1009,15 @@ int ldlm_pools_init(void)
 	int rc;
 
 	rc = ldlm_pools_thread_start();
-	if (rc)
-		return rc;
-
-	rc = register_shrinker(&ldlm_pools_cli_shrinker);
-	if (rc)
-		ldlm_pools_thread_stop();
+	if (!rc)
+		rc = register_shrinker(&ldlm_pools_cli_shrinker);
 
 	return rc;
 }
 
 void ldlm_pools_fini(void)
 {
-	if (ldlm_pools_thread)
-		unregister_shrinker(&ldlm_pools_cli_shrinker);
+	unregister_shrinker(&ldlm_pools_cli_shrinker);
 
 	ldlm_pools_thread_stop();
 }