[libcamera-devel] [PATCH v1 3/3] libcamerasrc: Fix deadlock on EOS

[Laurent Pinchart]

Hi Nicolas,

Thank you for the patch.

On Wed, Aug 25, 2021 at 05:18:52PM -0400, Nicolas Dufresne wrote:
> From: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> 
> It's not allowed in GStreamer to push events while holding the object
> lock. This reduce the scope into which we hold the object lock. In
> fact we don't need to protect against gst_task_resume() concurrency
> when we stop the task as resume only do something if the task is paused.

I've tried to check this, but overall I'll trust you on that as my
knowledge is limited here.

> This fixes a deadlock when running multiple instances of libcamerasrc
> and closing one of the streaming window.
> 
> Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
>  src/gstreamer/gstlibcamerasrc.cpp | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> index bdd9f88c..2be44edd 100644
> --- a/src/gstreamer/gstlibcamerasrc.cpp
> +++ b/src/gstreamer/gstlibcamerasrc.cpp
> @@ -312,12 +312,6 @@ gst_libcamera_src_task_run(gpointer user_data)
>  	}
>  
>  	{
> -		/*
> -		 * Here we need to decide if we want to pause or stop the task. This
> -		 * needs to happen in lock step with the callback thread which may want
> -		 * to resume the task.
> -		 */
> -		GLibLocker lock(GST_OBJECT(self));
>  		if (ret != GST_FLOW_OK) {
>  			if (ret == GST_FLOW_EOS) {
>  				g_autoptr(GstEvent) eos = gst_event_new_eos();
> @@ -332,6 +326,12 @@ gst_libcamera_src_task_run(gpointer user_data)
>  			return;
>  		}
>  
> +		/*
> +		 * Here we need to decide if we want to pause. This needs to
> +		 * happen in lock step with the callback thread which may want
> +		 * to resume the task and might push pending buffers.
> +		 */
> +		GLibLocker lock(GST_OBJECT(self));
>  		bool do_pause = true;
>  		for (GstPad *srcpad : state->srcpads_) {
>  			if (gst_libcamera_pad_has_pending(srcpad)) {

-- 
Regards,

Laurent Pinchart