Re: [PATCH v3 2/2] drm/msm/mdp5: Return error code in mdp5_mixer_release when deadlock is detected

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On 06/05/2022 00:40, Jessica Zhang wrote:
> There is a possibility for mdp5_get_global_state to return
> -EDEADLK when acquiring the modeset lock, but currently global_state in
> mdp5_mixer_release doesn't check for if an error is returned.
>
> To avoid a NULL dereference error, let's have mdp5_mixer_release
> check if an error is returned and propagate that error.
>
> 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_crtc.c  | 10 ++++++++--
>   drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.c | 15 +++++++++++----
>   drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.h |  4 ++--
>   3 files changed, 21 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> index b966cd69f99d..fe2922c8d21b 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> @@ -612,9 +612,15 @@ static int mdp5_crtc_setup_pipeline(struct drm_crtc *crtc,
>   		if (ret)
>   			return ret;
>   
> -		mdp5_mixer_release(new_crtc_state->state, old_mixer);
> +		ret = mdp5_mixer_release(new_crtc_state->state, old_mixer);
> +		if (ret)
> +			return ret;
> +
>   		if (old_r_mixer) {
> -			mdp5_mixer_release(new_crtc_state->state, old_r_mixer);
> +			ret = mdp5_mixer_release(new_crtc_state->state, old_r_mixer);
> +			if (ret)
> +				return ret;
> +
>   			if (!need_right_mixer)
>   				pipeline->r_mixer = NULL;
>   		}
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.c
> index 954db683ae44..2536def2a000 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.c
> @@ -116,21 +116,28 @@ int mdp5_mixer_assign(struct drm_atomic_state *s, struct drm_crtc *crtc,
>   	return 0;
>   }
>   
> -void mdp5_mixer_release(struct drm_atomic_state *s, struct mdp5_hw_mixer *mixer)
> +int mdp5_mixer_release(struct drm_atomic_state *s, struct mdp5_hw_mixer *mixer)
>   {
>   	struct mdp5_global_state *global_state = mdp5_get_global_state(s);
> -	struct mdp5_hw_mixer_state *new_state = &global_state->hwmixer;
> +	struct mdp5_hw_mixer_state *new_state;
>   
>   	if (!mixer)
> -		return;
> +		return 0;
> +
> +	if (IS_ERR(global_state))
> +		return PTR_ERR(global_state);
> +
> +	new_state = &global_state->hwmixer;
>   
>   	if (WARN_ON(!new_state->hwmixer_to_crtc[mixer->idx]))
> -		return;
> +		return -EINVAL;
>   
>   	DBG("%s: release from crtc %s", mixer->name,
>   	    new_state->hwmixer_to_crtc[mixer->idx]->name);
>   
>   	new_state->hwmixer_to_crtc[mixer->idx] = NULL;
> +
> +	return 0;
>   }
>   
>   void mdp5_mixer_destroy(struct mdp5_hw_mixer *mixer)
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.h b/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.h
> index 43c9ba43ce18..545ee223b9d7 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.h
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_mixer.h
> @@ -30,7 +30,7 @@ void mdp5_mixer_destroy(struct mdp5_hw_mixer *lm);
>   int mdp5_mixer_assign(struct drm_atomic_state *s, struct drm_crtc *crtc,
>   		      uint32_t caps, struct mdp5_hw_mixer **mixer,
>   		      struct mdp5_hw_mixer **r_mixer);
> -void mdp5_mixer_release(struct drm_atomic_state *s,
> -			struct mdp5_hw_mixer *mixer);
> +int mdp5_mixer_release(struct drm_atomic_state *s,
> +		       struct mdp5_hw_mixer *mixer);
>   
>   #endif /* __MDP5_LM_H__ */


--
With best wishes
Dmitry