Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 0e661006 authored by Hans Verkuil's avatar Hans Verkuil Committed by Mauro Carvalho Chehab
Browse files

[media] vb2: fix 'UNBALANCED' warnings when calling vb2_thread_stop() 



Stopping the vb2 thread (as used by several DVB devices) can result
in an 'UNBALANCED' warning such as this:

vb2: counters for queue ffff880407ee9828: UNBALANCED!
vb2:     setup: 1 start_streaming: 1 stop_streaming: 1
vb2:     wait_prepare: 249333 wait_finish: 249334

This is due to a race condition between stopping the thread and
calling vb2_internal_streamoff(). While I have not been able to deduce
the exact mechanism how this race condition can produce this warning,
I can see that the way the stream is stopped is likely to lead to a
race somewhere.

This patch simplifies how this is done by first ensuring that the
thread is completely stopped before cleaning up the vb2 queue. It
does that by setting threadio->stop to true, followed by a call to
vb2_queue_error() which will wake up the thread. The thread sees that
'stop' is true and it will exit.

The call to kthread_stop() waits until the thread has exited, and only
then is the queue cleaned up by calling __vb2_cleanup_fileio().

This is a much cleaner sequence and the warning has now disappeared.

Reported-by: default avatarJurgen Kramer <gtmkramer@xs4all.nl>
Tested-by: default avatarJurgen Kramer <gtmkramer@xs4all.nl>
Signed-off-by: default avatarHans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v3.18 and up
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@osg.samsung.com>
parent c517d838

drivers/media/v4l2-core/videobuf2-core.c

+3 −8
Original line number Diff line number Diff line
@@ -3230,18 +3230,13 @@ int vb2_thread_stop(struct vb2_queue *q) 


	if (threadio == NULL)

		return 0;

	call_void_qop(q, wait_finish, q);

	threadio->stop = true;

	vb2_internal_streamoff(q, q->type);

	call_void_qop(q, wait_prepare, q);

	/* Wake up all pending sleeps in the thread */

	vb2_queue_error(q);

	err = kthread_stop(threadio->thread);

	q->fileio = NULL;

	fileio->req.count = 0;

	vb2_reqbufs(q, &fileio->req);

	kfree(fileio);

	__vb2_cleanup_fileio(q);

	threadio->thread = NULL;

	kfree(threadio);

	q->fileio = NULL;

	q->threadio = NULL;

	return err;

}