Re: [PATCH 13/19] drm: simplify the locking in the GETCRTC ioctl

[Harry Wentland <harry.wentland@amd.com>]

On Wednesday, March 22, 2017 10:50:52 PM EDT Daniel Vetter wrote:
> No need to grab both plane and crtc locks at the same time, we can do
> them one after the other. If userspace races it'll get what it
> deserves either way.
> 
> This removes another user of drm_modeset_lock_crtc. There's only one
> left.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_crtc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 660b4c8715de..df1ff0b8818b 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -406,16 +406,18 @@ int drm_mode_getcrtc(struct drm_device *dev,
>  	if (!crtc)
>  		return -ENOENT;
> 
> -	drm_modeset_lock_crtc(crtc, crtc->primary);
>  	crtc_resp->gamma_size = crtc->gamma_size;
> 
> +	drm_modeset_lock(&crtc->primary->mutex, NULL);
>  	if (crtc->primary->state && crtc->primary->state->fb)
>  		crtc_resp->fb_id = crtc->primary->state->fb->base.id;
>  	else if (!crtc->primary->state && crtc->primary->fb)
>  		crtc_resp->fb_id = crtc->primary->fb->base.id;
>  	else
>  		crtc_resp->fb_id = 0;
> +	drm_modeset_unlock(&crtc->primary->mutex);
> 
> +	drm_modeset_lock(&crtc->mutex, NULL);
>  	if (crtc->state) {
>  		crtc_resp->x = crtc->primary->state->src_x >> 16;
>  		crtc_resp->y = crtc->primary->state->src_y >> 16;

What about crtc->primary here? Shouldn't that also be locked with the crtc-
>primary->mutex or do we treat state differently? Still not 100% on the exact 
locking semantics.

Harry

> @@ -437,7 +439,7 @@ int drm_mode_getcrtc(struct drm_device *dev,
>  			crtc_resp->mode_valid = 0;
>  		}
>  	}
> -	drm_modeset_unlock_crtc(crtc);
> +	drm_modeset_unlock(&crtc->mutex);
> 
>  	return 0;
>  }


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