Re: [PATCH] drm/vmwgfx: fix lock breakage

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Oct 30, 2014 at 01:39:04PM -0400, Rob Clark wrote:
> After:
> 
> commit d059f652e73c35678d28d4cd09ab2cec89696af9
> Author:     Daniel Vetter <daniel.vetter@ffwll.ch>
> AuthorDate: Fri Jul 25 18:07:40 2014 +0200
> 
>     drm: Handle legacy per-crtc locking with full acquire ctx
> 
> drm_mode_cursor_common() was switched to use drm_modeset_(un)lock_crtc()
> which uses full aquire ctx.  So dropping/reaquiring the lock via
> drm_modeset_(un)lock() directly isn't the right thing to do, as lockdep
> kindly points out.
> 
> The 'FIXME's about sorting out whether vmwgfx *really* needs to lock-all
> for cursor updates still apply.
> 
> Signed-off-by: Rob Clark <robdclark@gmail.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> index d2bc2b0..8fc1e38 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> @@ -187,7 +187,7 @@ int vmw_du_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
>  	 * can do this since the caller in the drm core doesn't check anything
>  	 * which is protected by any looks.
>  	 */
> -	drm_modeset_unlock(&crtc->mutex);
> +	drm_modeset_unlock_crtc(crtc);
>  	drm_modeset_lock_all(dev_priv->dev);

Oh right this is simpler, but it also grabs a new acquire context. So not
too terribly fair really, but otoh neither was the old one.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>  
>  	/* A lot of the code assumes this */
> @@ -252,7 +252,7 @@ int vmw_du_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
>  	ret = 0;
>  out:
>  	drm_modeset_unlock_all(dev_priv->dev);
> -	drm_modeset_lock(&crtc->mutex, NULL);
> +	drm_modeset_lock_crtc(crtc);
>  
>  	return ret;
>  }
> @@ -273,7 +273,7 @@ int vmw_du_crtc_cursor_move(struct drm_crtc *crtc, int x, int y)
>  	 * can do this since the caller in the drm core doesn't check anything
>  	 * which is protected by any looks.
>  	 */
> -	drm_modeset_unlock(&crtc->mutex);
> +	drm_modeset_unlock_crtc(crtc);
>  	drm_modeset_lock_all(dev_priv->dev);
>  
>  	vmw_cursor_update_position(dev_priv, shown,
> @@ -281,7 +281,7 @@ int vmw_du_crtc_cursor_move(struct drm_crtc *crtc, int x, int y)
>  				   du->cursor_y + du->hotspot_y);
>  
>  	drm_modeset_unlock_all(dev_priv->dev);
> -	drm_modeset_lock(&crtc->mutex, NULL);
> +	drm_modeset_lock_crtc(crtc);
>  
>  	return 0;
>  }
> -- 
> 1.9.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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