net/9p: replace p9_poll_task with a work

Now that cmwq can handle high concurrency, it's more efficient to use
work than a dedicated kthread.  Convert p9_poll_proc() to a work
function for p9_poll_work and make p9_pollwake() schedule it on each
poll event.  The work is sync flushed on module exit.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: v9fs-developer@lists.sourceforge.net

net/9p/trans_fd.c

@@ -153,9 +153,11 @@ struct p9_conn {
 	unsigned long wsched;
 };
 
+static void p9_poll_workfn(struct work_struct *work);
+
 static DEFINE_SPINLOCK(p9_poll_lock);
 static LIST_HEAD(p9_poll_pending_list);
-static struct task_struct *p9_poll_task;
+static DECLARE_WORK(p9_poll_work, p9_poll_workfn);
 
 static void p9_mux_poll_stop(struct p9_conn *m)
 {
@@ -515,15 +517,14 @@ static int p9_pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
 		container_of(wait, struct p9_poll_wait, wait);
 	struct p9_conn *m = pwait->conn;
 	unsigned long flags;
-	DECLARE_WAITQUEUE(dummy_wait, p9_poll_task);
 
 	spin_lock_irqsave(&p9_poll_lock, flags);
 	if (list_empty(&m->poll_pending_link))
 		list_add_tail(&m->poll_pending_link, &p9_poll_pending_list);
 	spin_unlock_irqrestore(&p9_poll_lock, flags);
 
-	/* perform the default wake up operation */
-	return default_wake_function(&dummy_wait, mode, sync, key);
+	schedule_work(&p9_poll_work);
+	return 1;
 }
 
 /**
@@ -1046,12 +1047,12 @@ static struct p9_trans_module p9_fd_trans = {
  *
  */
 
-static int p9_poll_proc(void *a)
+static void p9_poll_workfn(struct work_struct *work)
 {
 	unsigned long flags;
 
 	P9_DPRINTK(P9_DEBUG_TRANS, "start %p\n", current);
- repeat:
+
 	spin_lock_irqsave(&p9_poll_lock, flags);
 	while (!list_empty(&p9_poll_pending_list)) {
 		struct p9_conn *conn = list_first_entry(&p9_poll_pending_list,
@@ -1066,28 +1067,11 @@ static int p9_poll_proc(void *a)
 	}
 	spin_unlock_irqrestore(&p9_poll_lock, flags);
 
-	set_current_state(TASK_INTERRUPTIBLE);
-	if (list_empty(&p9_poll_pending_list)) {
-		P9_DPRINTK(P9_DEBUG_TRANS, "sleeping...\n");
-		schedule();
-	}
-	__set_current_state(TASK_RUNNING);
-
-	if (!kthread_should_stop())
-		goto repeat;
-
 	P9_DPRINTK(P9_DEBUG_TRANS, "finish\n");
-	return 0;
 }
 
 int p9_trans_fd_init(void)
 {
-	p9_poll_task = kthread_run(p9_poll_proc, NULL, "v9fs-poll");
-	if (IS_ERR(p9_poll_task)) {
-		printk(KERN_WARNING "v9fs: mux: creating poll task failed\n");
-		return PTR_ERR(p9_poll_task);
-	}
-
 	v9fs_register_trans(&p9_tcp_trans);
 	v9fs_register_trans(&p9_unix_trans);
 	v9fs_register_trans(&p9_fd_trans);
@@ -1097,7 +1081,7 @@ int p9_trans_fd_init(void)
 
 void p9_trans_fd_exit(void)
 {
-	kthread_stop(p9_poll_task);
+	flush_work_sync(&p9_poll_work);
 	v9fs_unregister_trans(&p9_tcp_trans);
 	v9fs_unregister_trans(&p9_unix_trans);
 	v9fs_unregister_trans(&p9_fd_trans);