V4L/DVB: fix dvb frontend lockup

If my dvb device is removed while in use, I got the following oops:

[ 4920.484084] Call Trace:
[ 4920.484102]  [<c102daad>] ? default_wake_function+0x0/0x8
[ 4920.484147]  [<f8cb09e1>] ? dvb_unregister_frontend+0x95/0xcc [dvb_core]
[ 4920.484157]  [<c1044412>] ? autoremove_wake_function+0x0/0x2d
[ 4920.484168]  [<f8dd1af2>] ? dvb_usb_adapter_frontend_exit+0x12/0x21 [dvb_usb]
[ 4920.484176]  [<f8dd12f1>] ? dvb_usb_exit+0x26/0x88 [dvb_usb]
[ 4920.484184]  [<f8dd138d>] ? dvb_usb_device_exit+0x3a/0x4a [dvb_usb]
[ 4920.484217]  [<f7fe1b08>] ? usb_unbind_interface+0x3f/0xb4 [usbcore]
[ 4920.484227]  [<c11a4178>] ? __device_release_driver+0x74/0xb7
[ 4920.484233]  [<c11a4247>] ? device_release_driver+0x15/0x1e
[ 4920.484243]  [<c11a3a33>] ? bus_remove_device+0x6e/0x87
[ 4920.484249]  [<c11a26d6>] ? device_del+0xfa/0x152
[ 4920.484264]  [<f7fdf609>] ? usb_disable_device+0x59/0xb9 [usbcore]
[ 4920.484279]  [<f7fdb9ee>] ? usb_disconnect+0x70/0xdc [usbcore]
[ 4920.484294]  [<f7fdc728>] ? hub_thread+0x521/0xe1d [usbcore]
[ 4920.484301]  [<c1044412>] ? autoremove_wake_function+0x0/0x2d
[ 4920.484316]  [<f7fdc207>] ? hub_thread+0x0/0xe1d [usbcore]
[ 4920.484321]  [<c10441e0>] ? kthread+0x61/0x66
[ 4920.484327]  [<c104417f>] ? kthread+0x0/0x66
[ 4920.484336]  [<c1003d47>] ? kernel_thread_helper+0x7/0x10

If there are users (for example users == -2) :
 - dvb_unregister_frontend :
 - stop kernel thread with dvb_frontend_stop :
  - fepriv->exit = 1;
  - thread loop catch stop event and break while loop
  - fepriv->thread = NULL; and fepriv->exit = 0;
 - dvb_unregister_frontend wait on "fepriv->dvbdev->wait_queue" that fepriv->dvbdev->users==-1.
The user finish :
 - dvb_frontend_release - set users to -1
 - don't wait wait_queue because fepriv->exit != 1

=> dvb_unregister_frontend never exit the wait queue.
Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/dvb-core/dvb_frontend.c

@@ -95,6 +95,10 @@ MODULE_PARM_DESC(dvb_mfe_wait_time, "Wait up to <mfe_wait_time> seconds on open(
  * FESTATE_LOSTLOCK. When the lock has been lost, and we're searching it again.
  */
 
+#define DVB_FE_NO_EXIT	0
+#define DVB_FE_NORMAL_EXIT	1
+#define DVB_FE_DEVICE_REMOVED	2
+
 static DEFINE_MUTEX(frontend_mutex);
 
 struct dvb_frontend_private {
@@ -497,7 +501,7 @@ static int dvb_frontend_is_exiting(struct dvb_frontend *fe)
 {
 	struct dvb_frontend_private *fepriv = fe->frontend_priv;
 
-	if (fepriv->exit)
+	if (fepriv->exit != DVB_FE_NO_EXIT)
 		return 1;
 
 	if (fepriv->dvbdev->writers == 1)
@@ -559,7 +563,7 @@ static int dvb_frontend_thread(void *data)
 
 		if (kthread_should_stop() || dvb_frontend_is_exiting(fe)) {
 			/* got signal or quitting */
-			fepriv->exit = 1;
+			fepriv->exit = DVB_FE_NORMAL_EXIT;
 			break;
 		}
 
@@ -673,7 +677,10 @@ static int dvb_frontend_thread(void *data)
 	}
 
 	fepriv->thread = NULL;
-	fepriv->exit = 0;
+	if (kthread_should_stop())
+		fepriv->exit = DVB_FE_DEVICE_REMOVED;
+	else
+		fepriv->exit = DVB_FE_NO_EXIT;
 	mb();
 
 	dvb_frontend_wakeup(fe);
@@ -686,7 +693,7 @@ static void dvb_frontend_stop(struct dvb_frontend *fe)
 
 	dprintk ("%s\n", __func__);
 
-	fepriv->exit = 1;
+	fepriv->exit = DVB_FE_NORMAL_EXIT;
 	mb();
 
 	if (!fepriv->thread)
@@ -755,7 +762,7 @@ static int dvb_frontend_start(struct dvb_frontend *fe)
 	dprintk ("%s\n", __func__);
 
 	if (fepriv->thread) {
-		if (!fepriv->exit)
+		if (fepriv->exit == DVB_FE_NO_EXIT)
 			return 0;
 		else
 			dvb_frontend_stop (fe);
@@ -767,7 +774,7 @@ static int dvb_frontend_start(struct dvb_frontend *fe)
 		return -EINTR;
 
 	fepriv->state = FESTATE_IDLE;
-	fepriv->exit = 0;
+	fepriv->exit = DVB_FE_NO_EXIT;
 	fepriv->thread = NULL;
 	mb();
 
@@ -1490,7 +1497,7 @@ static int dvb_frontend_ioctl(struct inode *inode, struct file *file,
 
 	dprintk("%s (%d)\n", __func__, _IOC_NR(cmd));
 
-	if (fepriv->exit)
+	if (fepriv->exit != DVB_FE_NO_EXIT)
 		return -ENODEV;
 
 	if ((file->f_flags & O_ACCMODE) == O_RDONLY &&
@@ -1916,6 +1923,8 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 	int ret;
 
 	dprintk ("%s\n", __func__);
+	if (fepriv->exit == DVB_FE_DEVICE_REMOVED)
+		return -ENODEV;
 
 	if (adapter->mfe_shared) {
 		mutex_lock (&adapter->mfe_lock);
@@ -2008,7 +2017,7 @@ static int dvb_frontend_release(struct inode *inode, struct file *file)
 	ret = dvb_generic_release (inode, file);
 
 	if (dvbdev->users == -1) {
-		if (fepriv->exit == 1) {
+		if (fepriv->exit != DVB_FE_NO_EXIT) {
 			fops_put(file->f_op);
 			file->f_op = NULL;
 			wake_up(&dvbdev->wait_queue);