Re: [PATCH v3 1/2] drm/msm/mdp5: Return error code in mdp5_pipe_release when deadlock is detected

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On 06/05/2022 00:40, Jessica Zhang wrote:
> mdp5_get_global_state runs the risk of hitting a -EDEADLK when acquiring
> the modeset lock, but currently mdp5_pipe_release doesn't check for if
> an error is returned. Because of this, there is a possibility of
> mdp5_pipe_release hitting a NULL dereference error.
>
> To avoid this, let's have mdp5_pipe_release check if
> mdp5_get_global_state returns an error and propogate that error.
>
> Changes since v1:
> - Separated declaration and initialization of *new_state to avoid
>    compiler warning
> - Fixed some spelling mistakes in commit message
>
> Changes since v2:
> - Return 0 in case where hwpipe is NULL as this is considered normal
>    behavior
> - Added 2nd patch in series to fix a similar NULL dereference issue in
>    mdp5_mixer_release
>
> Reported-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> Signed-off-by: Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> ---
>   drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c  | 15 +++++++++++----
>   drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.h  |  2 +-
>   drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 20 ++++++++++++++++----
>   3 files changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
> index ba6695963aa6..a4f5cb90f3e8 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.c
> @@ -119,18 +119,23 @@ int mdp5_pipe_assign(struct drm_atomic_state *s, struct drm_plane *plane,
>   	return 0;
>   }
>   
> -void mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe)
> +int mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe)
>   {
>   	struct msm_drm_private *priv = s->dev->dev_private;
>   	struct mdp5_kms *mdp5_kms = to_mdp5_kms(to_mdp_kms(priv->kms));
>   	struct mdp5_global_state *state = mdp5_get_global_state(s);
> -	struct mdp5_hw_pipe_state *new_state = &state->hwpipe;
> +	struct mdp5_hw_pipe_state *new_state;
>   
>   	if (!hwpipe)
> -		return;
> +		return 0;
> +
> +	if (IS_ERR(state))
> +		return PTR_ERR(state);
> +
> +	new_state = &state->hwpipe;
>   
>   	if (WARN_ON(!new_state->hwpipe_to_plane[hwpipe->idx]))
> -		return;
> +		return -EINVAL;
>   
>   	DBG("%s: release from plane %s", hwpipe->name,
>   		new_state->hwpipe_to_plane[hwpipe->idx]->name);
> @@ -141,6 +146,8 @@ void mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe)
>   	}
>   
>   	new_state->hwpipe_to_plane[hwpipe->idx] = NULL;
> +
> +	return 0;
>   }
>   
>   void mdp5_pipe_destroy(struct mdp5_hw_pipe *hwpipe)
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.h b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.h
> index 9b26d0761bd4..cca67938cab2 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.h
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_pipe.h
> @@ -37,7 +37,7 @@ int mdp5_pipe_assign(struct drm_atomic_state *s, struct drm_plane *plane,
>   		     uint32_t caps, uint32_t blkcfg,
>   		     struct mdp5_hw_pipe **hwpipe,
>   		     struct mdp5_hw_pipe **r_hwpipe);
> -void mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe);
> +int mdp5_pipe_release(struct drm_atomic_state *s, struct mdp5_hw_pipe *hwpipe);
>   
>   struct mdp5_hw_pipe *mdp5_pipe_init(enum mdp5_pipe pipe,
>   		uint32_t reg_offset, uint32_t caps);
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> index 228b22830970..979458482841 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
> @@ -311,12 +311,24 @@ static int mdp5_plane_atomic_check_with_state(struct drm_crtc_state *crtc_state,
>   				mdp5_state->r_hwpipe = NULL;
>   
>   
> -			mdp5_pipe_release(state->state, old_hwpipe);
> -			mdp5_pipe_release(state->state, old_right_hwpipe);
> +			ret = mdp5_pipe_release(state->state, old_hwpipe);
> +			if (ret)
> +				return ret;
> +
> +			ret = mdp5_pipe_release(state->state, old_right_hwpipe);
> +			if (ret)
> +				return ret;
> +
>   		}
>   	} else {
> -		mdp5_pipe_release(state->state, mdp5_state->hwpipe);
> -		mdp5_pipe_release(state->state, mdp5_state->r_hwpipe);
> +		ret = mdp5_pipe_release(state->state, mdp5_state->hwpipe);
> +		if (ret)
> +			return ret;
> +
> +		ret = mdp5_pipe_release(state->state, mdp5_state->r_hwpipe);
> +		if (ret)
> +			return ret;
> +
>   		mdp5_state->hwpipe = mdp5_state->r_hwpipe = NULL;
>   	}
>   


--
With best wishes
Dmitry