usbip: event handler as one thread

Dear all,

1. Overview

In current USB/IP implementation, event kernel threads are created for
each port. The functions of the threads are closing connection and
error handling so they don't have not so many events to handle. There's
no need to have thread for each port.

BEFORE) vhci side - VHCI_NPORTS(8) threads are created.
$ ps aux | grep usbip
root     10059  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10060  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10061  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10062  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10063  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10064  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10065  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]
root     10066  0.0  0.0      0     0 ?        S    17:06   0:00 [usbip_eh]

BEFORE) stub side - threads will be created every bind operation.
$ ps aux | grep usbip
root      8368  0.0  0.0      0     0 ?        S    17:56   0:00 [usbip_eh]
root      8399  0.0  0.0      0     0 ?        S    17:56   0:00 [usbip_eh]

This patch put event threads of stub and vhci driver as one workqueue.

AFTER) only one event threads in each vhci and stub side.
$ ps aux | grep usbip
root     10457  0.0  0.0      0     0 ?        S<   17:47   0:00 [usbip_event]

2. Modification to usbip_event.c

BEFORE) kernel threads are created in usbip_start_eh().

AFTER) one workqueue is created in new usbip_init_eh().

Event handler which was main loop of kernel thread is modified to
workqueue handler.

Events themselves are stored in struct usbip_device - same as before.
usbip_devices which have event are listed in event_list.

The handler picks an element from the list and wakeup usbip_device. The
wakeup method is same as before.

usbip_in_eh() substitutes statement which checks whether functions are
called from eh_ops or not. In this function, the worker context is used
for the checking. The context will be set in a variable in the
beginning of first event handling. usbip_in_eh() is used in event
handler so it works well.

3. Modifications to programs using usbip_event.c

Initialization and termination of workqueue are added to init and exit
routine of usbip_core respectively.

A. version info

v2)
# Merged 1/2 event handler itself and 2/2 user programs because of auto
build fail at 1/2 casued unmodified user programs in 1/2.
Signed-off-by: Nobuo Iwata <nobuo.iwata@fujixerox.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/stub_dev.c

@@ -388,7 +388,6 @@ static int stub_probe(struct usb_device *udev)
 err_port:
 	dev_set_drvdata(&udev->dev, NULL);
 	usb_put_dev(udev);
-	kthread_stop_put(sdev->ud.eh);
 
 	busid_priv->sdev = NULL;
 	stub_device_free(sdev);
@@ -449,7 +448,7 @@ static void stub_disconnect(struct usb_device *udev)
 	}
 
 	/* If usb reset is called from event handler */
-	if (busid_priv->sdev->ud.eh == current)
+	if (usbip_in_eh(current))
 		return;
 
 	/* shutdown the current connection */

drivers/usb/usbip/usbip_common.c

@@ -769,12 +769,19 @@ EXPORT_SYMBOL_GPL(usbip_recv_xbuff);
 
 static int __init usbip_core_init(void)
 {
+	int ret;
+
 	pr_info(DRIVER_DESC " v" USBIP_VERSION "\n");
+	ret = usbip_init_eh();
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
 static void __exit usbip_core_exit(void)
 {
+	usbip_finish_eh();
 	return;
 }
 

drivers/usb/usbip/usbip_common.h

@@ -267,7 +267,6 @@ struct usbip_device {
 	struct task_struct *tcp_tx;
 
 	unsigned long event;
-	struct task_struct *eh;
 	wait_queue_head_t eh_waitq;
 
 	struct eh_ops {
@@ -313,10 +312,13 @@ void usbip_pad_iso(struct usbip_device *ud, struct urb *urb);
 int usbip_recv_xbuff(struct usbip_device *ud, struct urb *urb);
 
 /* usbip_event.c */
+int usbip_init_eh(void);
+void usbip_finish_eh(void);
 int usbip_start_eh(struct usbip_device *ud);
 void usbip_stop_eh(struct usbip_device *ud);
 void usbip_event_add(struct usbip_device *ud, unsigned long event);
 int usbip_event_happened(struct usbip_device *ud);
+int usbip_in_eh(struct task_struct *task);
 
 static inline int interface_to_busnum(struct usb_interface *interface)
 {

drivers/usb/usbip/usbip_event.c

 /*
  * Copyright (C) 2003-2008 Takahiro Hirofuchi
+ * Copyright (C) 2015 Nobuo Iwata
  *
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -19,17 +20,68 @@
 
 #include <linux/kthread.h>
 #include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
 
 #include "usbip_common.h"
 
-static int event_handler(struct usbip_device *ud)
+struct usbip_event {
+	struct list_head node;
+	struct usbip_device *ud;
+};
+
+static DEFINE_SPINLOCK(event_lock);
+static LIST_HEAD(event_list);
+
+static void set_event(struct usbip_device *ud, unsigned long event)
 {
-	usbip_dbg_eh("enter\n");
+	unsigned long flags;
 
-	/*
-	 * Events are handled by only this thread.
-	 */
-	while (usbip_event_happened(ud)) {
+	spin_lock_irqsave(&ud->lock, flags);
+	ud->event |= event;
+	spin_unlock_irqrestore(&ud->lock, flags);
+}
+
+static void unset_event(struct usbip_device *ud, unsigned long event)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&ud->lock, flags);
+	ud->event &= ~event;
+	spin_unlock_irqrestore(&ud->lock, flags);
+}
+
+static struct usbip_device *get_event(void)
+{
+	struct usbip_event *ue = NULL;
+	struct usbip_device *ud = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(&event_lock, flags);
+	if (!list_empty(&event_list)) {
+		ue = list_first_entry(&event_list, struct usbip_event, node);
+		list_del(&ue->node);
+	}
+	spin_unlock_irqrestore(&event_lock, flags);
+
+	if (ue) {
+		ud = ue->ud;
+		kfree(ue);
+	}
+	return ud;
+}
+
+static struct task_struct *worker_context;
+
+static void event_handler(struct work_struct *work)
+{
+	struct usbip_device *ud;
+
+	if (worker_context == NULL) {
+		worker_context = current;
+	}
+
+	while ((ud = get_event()) != NULL) {
 		usbip_dbg_eh("pending event %lx\n", ud->event);
 
 		/*
@@ -38,79 +90,102 @@ static int event_handler(struct usbip_device *ud)
 		 */
 		if (ud->event & USBIP_EH_SHUTDOWN) {
 			ud->eh_ops.shutdown(ud);
-			ud->event &= ~USBIP_EH_SHUTDOWN;
+			unset_event(ud, USBIP_EH_SHUTDOWN);
 		}
 
 		/* Reset the device. */
 		if (ud->event & USBIP_EH_RESET) {
 			ud->eh_ops.reset(ud);
-			ud->event &= ~USBIP_EH_RESET;
+			unset_event(ud, USBIP_EH_RESET);
 		}
 
 		/* Mark the device as unusable. */
 		if (ud->event & USBIP_EH_UNUSABLE) {
 			ud->eh_ops.unusable(ud);
-			ud->event &= ~USBIP_EH_UNUSABLE;
+			unset_event(ud, USBIP_EH_UNUSABLE);
 		}
 
 		/* Stop the error handler. */
 		if (ud->event & USBIP_EH_BYE)
-			return -1;
+			usbip_dbg_eh("removed %p\n", ud);
+
+		wake_up(&ud->eh_waitq);
 	}
+}
 
+int usbip_start_eh(struct usbip_device *ud)
+{
+	init_waitqueue_head(&ud->eh_waitq);
+	ud->event = 0;
 	return 0;
 }
+EXPORT_SYMBOL_GPL(usbip_start_eh);
 
-static int event_handler_loop(void *data)
+void usbip_stop_eh(struct usbip_device *ud)
 {
-	struct usbip_device *ud = data;
+	unsigned long pending = ud->event & ~USBIP_EH_BYE;
 
-	while (!kthread_should_stop()) {
-		wait_event_interruptible(ud->eh_waitq,
-					 usbip_event_happened(ud) ||
-					 kthread_should_stop());
-		usbip_dbg_eh("wakeup\n");
+	if (!(ud->event & USBIP_EH_BYE))
+		usbip_dbg_eh("usbip_eh stopping but not removed\n");
 
-		if (event_handler(ud) < 0)
-			break;
-	}
+	if (pending)
+		usbip_dbg_eh("usbip_eh waiting completion %lx\n", pending);
 
-	return 0;
+	wait_event_interruptible(ud->eh_waitq, !(ud->event & ~USBIP_EH_BYE));
+	usbip_dbg_eh("usbip_eh has stopped\n");
 }
+EXPORT_SYMBOL_GPL(usbip_stop_eh);
 
-int usbip_start_eh(struct usbip_device *ud)
-{
-	init_waitqueue_head(&ud->eh_waitq);
-	ud->event = 0;
+#define WORK_QUEUE_NAME "usbip_event"
 
-	ud->eh = kthread_run(event_handler_loop, ud, "usbip_eh");
-	if (IS_ERR(ud->eh)) {
-		pr_warn("Unable to start control thread\n");
-		return PTR_ERR(ud->eh);
-	}
+static struct workqueue_struct *usbip_queue;
+static DECLARE_WORK(usbip_work, event_handler);
 
+int usbip_init_eh(void)
+{
+	usbip_queue = create_singlethread_workqueue(WORK_QUEUE_NAME);
+	if (usbip_queue == NULL) {
+		pr_err("failed to create usbip_event\n");
+		return -ENOMEM;
+	}
 	return 0;
 }
-EXPORT_SYMBOL_GPL(usbip_start_eh);
 
-void usbip_stop_eh(struct usbip_device *ud)
+void usbip_finish_eh(void)
 {
-	if (ud->eh == current)
-		return; /* do not wait for myself */
-
-	kthread_stop(ud->eh);
-	usbip_dbg_eh("usbip_eh has finished\n");
+	flush_workqueue(usbip_queue);
+	destroy_workqueue(usbip_queue);
+	usbip_queue = NULL;
 }
-EXPORT_SYMBOL_GPL(usbip_stop_eh);
 
 void usbip_event_add(struct usbip_device *ud, unsigned long event)
 {
+	struct usbip_event *ue;
 	unsigned long flags;
 
-	spin_lock_irqsave(&ud->lock, flags);
-	ud->event |= event;
-	wake_up(&ud->eh_waitq);
-	spin_unlock_irqrestore(&ud->lock, flags);
+	if (ud->event & USBIP_EH_BYE)
+		return;
+
+	set_event(ud, event);
+
+	spin_lock_irqsave(&event_lock, flags);
+
+	list_for_each_entry_reverse(ue, &event_list, node) {
+		if (ue->ud == ud)
+			goto out;
+	}
+
+	ue = kmalloc(sizeof(struct usbip_event), GFP_ATOMIC);
+	if (ue == NULL)
+		goto out;
+
+	ue->ud = ud;
+
+	list_add_tail(&ue->node, &event_list);
+	queue_work(usbip_queue, &usbip_work);
+
+out:
+	spin_unlock_irqrestore(&event_lock, flags);
 }
 EXPORT_SYMBOL_GPL(usbip_event_add);
 
@@ -127,3 +202,12 @@ int usbip_event_happened(struct usbip_device *ud)
 	return happened;
 }
 EXPORT_SYMBOL_GPL(usbip_event_happened);
+
+int usbip_in_eh(struct task_struct *task)
+{
+	if (task == worker_context)
+		return 1;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usbip_in_eh);