linux-kernel - Re: [PATCH] i915: don't call drm_atomic_state

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Message-ID: <20161018152908.GI3759@imgtec.com>
Date:   Tue, 18 Oct 2016 16:29:08 +0100
From:   Eric Engestrom <eric.engestrom@...tec.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        "Ander Conselvan de Oliveira" <ander.conselvan.de.oliveira@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH] i915: don't call drm_atomic_state_put on invalid pointer

On Tuesday, 2016-10-18 17:16:23 +0200, Arnd Bergmann wrote:
> The introduction of reference counting on the state structures caused
> sanitize_watermarks() in i915 to break in the error handling case,
> as pointed out by gcc -Wmaybe-uninitialized
> 
> drivers/gpu/drm/i915/intel_display.c: In function ‘intel_modeset_init’:
> include/drm/drm_atomic.h:224:2: error: ‘state’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This changes the function back to only drop the reference count
> when it was successfully allocated first.
> 
> Fixes: 0853695c3ba4 ("drm: Add reference counting to drm_atomic_state")
> Cc: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Eric Engestrom <eric.engestrom@...tec.com>

> ---
>  drivers/gpu/drm/i915/intel_display.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 6d168685bbda..6a26da143aa6 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -16314,7 +16314,7 @@ static void sanitize_watermarks(struct drm_device *dev)
>  		 * BIOS-programmed watermarks untouched and hope for the best.
>  		 */
>  		WARN(true, "Could not determine valid watermarks for inherited state\n");
> -		goto fail;
> +		goto put_state;
>  	}
>  
>  	/* Write calculated watermark values back */
> @@ -16325,8 +16325,9 @@ static void sanitize_watermarks(struct drm_device *dev)
>  		dev_priv->display.optimize_watermarks(cs);
>  	}
>  
> -fail:
> +put_state:
>  	drm_atomic_state_put(state);
> +fail:
>  	drm_modeset_drop_locks(&ctx);
>  	drm_modeset_acquire_fini(&ctx);
>  }
> -- 
> 2.9.0