V4L/DVB (7321): pvrusb2: Rework context handling and initialization

This change significantly rearranges pvr2_context level initialization
and operation:

1. A new kernel thread is set up for management of the context.

2. Destruction of the pvr2_context instance is moved into the kernel
   thread.  No other context is able to remove the instance; doing
   this simplifies lock handling.

3. The callback into pvrusb2-main, which is used to trigger
   initialization of each interface, is now issued from this kernel
   thread.  Previously it had been indirectly issued out of the work
   queue thread in pvr2_hdw, which led to deadlock issues if the
   interface needed to change a control setting (which in turn
   requires dispatch of another work queue entry).

4. Callbacks into the interfaces (via the pvr2_channel structure) are
   now issued strictly from this thread.  The net result of this is
   that such callback functions can now also safely operate driver
   controls without deadlocking the work queue.  (At the moment this
   is not actually a problem, but I'm anticipating issues with this in
   the future).

5. There is no longer any need for anyone to enter / exit the
   pvr2_context structure.  Implementation of the kernel thread here
   allows this all to be internal now, simplifying other logic.

6. A very very longstanding issue involving a mutex deadlock between
   the pvrusb2 driver and v4l should now be solved.  The deadlock
   involved the pvr2_context mutex and a globals-protecting mutex in
   v4l.  During initialization the driver would take the pvr2_context
   mutex first then the v4l2 interface would register with v4l and
   implicitly take the v4l mutex.  Later when v4l would call back into
   the driver, the two mutexes could possibly be taken in the opposite
   order, a situation that can lead to deadlock.  In practice this
   really wasn't an issue unless a v4l app tried to start VERY early
   after the driver appeared.  However it still needed to be solved,
   and with the use of the kernel thread relieving need for
   pvr2_context mutex, the problem should be finally solved.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 5 insertions, 15 deletions

diff --git a/drivers/media/video/pvrusb2/pvrusb2-hdw.c b/drivers/media/video/pvrusb2/pvrusb2-hdw.c
index 1dff2d04a5d..7e7c570cf83 100644
--- a/drivers/media/video/pvrusb2/pvrusb2-hdw.c
+++ b/drivers/media/video/pvrusb2/pvrusb2-hdw.c
@@ -221,7 +221,6 @@ static int pvr2_hdw_state_eval(struct pvr2_hdw *);
 static void pvr2_hdw_set_cur_freq(struct pvr2_hdw *,unsigned long);
 static void pvr2_hdw_worker_i2c(struct work_struct *work);
 static void pvr2_hdw_worker_poll(struct work_struct *work);
-static void pvr2_hdw_worker_init(struct work_struct *work);
 static int pvr2_hdw_wait(struct pvr2_hdw *,int state);
 static int pvr2_hdw_untrip_unlocked(struct pvr2_hdw *);
 static void pvr2_hdw_state_log_state(struct pvr2_hdw *);
@@ -1816,15 +1815,16 @@ static void pvr2_hdw_setup(struct pvr2_hdw *hdw)
 /* Perform second stage initialization.  Set callback pointer first so that
    we can avoid a possible initialization race (if the kernel thread runs
    before the callback has been set). */
-void pvr2_hdw_initialize(struct pvr2_hdw *hdw,
-			 void (*callback_func)(void *),
-			 void *callback_data)
+int pvr2_hdw_initialize(struct pvr2_hdw *hdw,
+			void (*callback_func)(void *),
+			void *callback_data)
 {
 	LOCK_TAKE(hdw->big_lock); do {
 		hdw->state_data = callback_data;
 		hdw->state_func = callback_func;
 	} while (0); LOCK_GIVE(hdw->big_lock);
-	queue_work(hdw->workqueue,&hdw->workinit);
+	pvr2_hdw_setup(hdw);
+	return hdw->flag_init_ok;
 }
 
 
@@ -2032,7 +2032,6 @@ struct pvr2_hdw *pvr2_hdw_create(struct usb_interface *intf,
 	hdw->workqueue = create_singlethread_workqueue(hdw->name);
 	INIT_WORK(&hdw->workpoll,pvr2_hdw_worker_poll);
 	INIT_WORK(&hdw->worki2csync,pvr2_hdw_worker_i2c);
-	INIT_WORK(&hdw->workinit,pvr2_hdw_worker_init);
 
 	pvr2_trace(PVR2_TRACE_INIT,"Driver unit number is %d, name is %s",
 		   hdw->unit_number,hdw->name);
@@ -2517,15 +2516,6 @@ static void pvr2_hdw_worker_poll(struct work_struct *work)
 }
 
 
-static void pvr2_hdw_worker_init(struct work_struct *work)
-{
-	struct pvr2_hdw *hdw = container_of(work,struct pvr2_hdw,workinit);
-	LOCK_TAKE(hdw->big_lock); do {
-		pvr2_hdw_setup(hdw);
-	} while (0); LOCK_GIVE(hdw->big_lock);
-}
-
-
 static int pvr2_hdw_wait(struct pvr2_hdw *hdw,int state)
 {
 	return wait_event_interruptible(