Hello Me.
Ok, so a bit of investigation into *why* we have an unbalanced
media_pipeline stop call.
After a suspend/resume cycle, the function vsp1_pm_runtime_resume() is
called by the PM framework.
The hardware is unable to reset successfully and the reset call returns
-ETIMEDOUT which gets passed back to the PM framework as a failure and
thus the device is not 'resumed'
This process is commenced, as the DU driver tries to enable the VSP, we
get the following call stack:
rcar_du_crtc_resume()
rcar_du_vsp_enable()
vsp1_du_setup_lif() // returns void
vsp1_device_get() // returns -ETIMEDOUT,
As the vsp1_du_setup_lif() returns void, the fact that the hardware
failed to start is ignored.
Later we get a call to rcar_du_vsp_disable(), which again calls into
vsp1_du_setup_lif(), this time to disable the pipeline. And it is here,
that the call to media_pipeline_stop() is an unbalanced call, as the
corresponding media_pipeline_start() would only have been called if the
vsp1_device_get() had succeeded, thus we find ourselves with a kernel
panic on a null dereference.
Sorry for the terse notes, they are possibly/probably really for me if I
get tasked to look back at this.
--
Regards
Kieran
On 13/12/16 17:59, Kieran Bingham wrote:
> media_entity_pipeline_stop() can be called through error paths with a
> NULL entity pipe object. In this instance, stopping is a no-op, so
> simply return without any action
>
> Signed-off-by: Kieran Bingham <kieran.bingham+rene...@ideasonboard.com>
> ---
>
> I've marked this patch as RFC, although if deemed suitable, by all means
> integrate it as is.
>
> When testing suspend/resume operations on VSP1, I encountered a segfault on
> the
> WARN_ON(!pipe->streaming_count) line, where 'pipe == NULL'. The simple
> protection fix is to return early in this instance, as this patch does
> however:
>
> A) Does this early return path warrant a WARN() statement itself, to identify
> drivers which are incorrectly calling media_entity_pipeline_stop() with an
> invalid entity, or would this just be noise ...
>
> and therefore..
>
> B) I also partly assume this patch could simply get NAK'd with a request to go
> and dig out the root cause of calling media_entity_pipeline_stop() with an
> invalid entity.
>
> My brief investigation so far here so far shows that it's almost a second
> order
> fault - where the first suspend resume cycle completes but leaves the entity
> in
> an invalid state having followed an error path - and then on a second
> suspend/resume - the stop fails with the affected segfault.
>
> If statement A) or B) apply here, please drop this patch from the series, and
> don't consider it a blocking issue for the other 3 patches.
>
> Kieran
>
>
> drivers/media/media-entity.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> index c68239e60487..93c9cbf4bf46 100644
> --- a/drivers/media/media-entity.c
> +++ b/drivers/media/media-entity.c
> @@ -508,6 +508,8 @@ void __media_entity_pipeline_stop(struct media_entity
> *entity)
> struct media_entity_graph *graph = &entity->pipe->graph;
> struct media_pipeline *pipe = entity->pipe;
>
> + if (!pipe)
> + return;
>
> WARN_ON(!pipe->streaming_count);
> media_entity_graph_walk_start(graph, entity);
>
