linux-kernel - Re: [PATCH][V2] drm/i915/guc: fix GEM_BUG

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Date:   Tue, 12 Jun 2018 12:10:16 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V2] drm/i915/guc: fix GEM_BUG_ON check

On Mon, Jun 11, 2018 at 05:46:53PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The check for level being less than zero always false because flags
> is currently unsigned and can never be negative. Fix this by making
> flags a s32.
> 
> Detected by CoverityScan, CID#1468363 ("Macro compares unsigned to 0")
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> 
> ---
> V2: Make flags s32 rather than remove the GEM_BUG_ON check, thanks to
> Ville Syrjälä for spotting the mistake in my first attempt.
> ---
>  drivers/gpu/drm/i915/intel_guc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_guc.c b/drivers/gpu/drm/i915/intel_guc.c
> index 116f4ccf1bbd..fb31f5004bcf 100644
> --- a/drivers/gpu/drm/i915/intel_guc.c
> +++ b/drivers/gpu/drm/i915/intel_guc.c
> @@ -206,7 +206,7 @@ void intel_guc_fini(struct intel_guc *guc)
>  static u32 get_log_control_flags(void)
>  {
>  	u32 level = i915_modparams.guc_log_level;
> -	u32 flags = 0;
> +	s32 flags = 0;
>  
>  	GEM_BUG_ON(level < 0);

Only insane people use "s32" when it's not part of the hardware spec and
you changed the wrong variable...

regards,
dan carpenter