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: Jurgen Kramer <gtmkramer@xxxxxxxxx> Tested-by: Jurgen Kramer <gtmkramer@xxxxxxxxx> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # for v3.18 and up --- drivers/media/v4l2-core/videobuf2-core.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c index bc08a82..cc16e76 100644 --- a/drivers/media/v4l2-core/videobuf2-core.c +++ b/drivers/media/v4l2-core/videobuf2-core.c @@ -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; } -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
