[Intel-gfx] [PATCH] drm/i915/display: Fix early deref of 'dsb'

[Manna, Animesh]

On 25-05-2020 05:09, Chris Wilson wrote:
> drivers/gpu/drm/i915/display/intel_dsb.c:177 intel_dsb_reg_write() warn: variable dereferenced before check 'dsb' (see line 175)
>
> Fixes: afeda4f3b1c8 ("drm/i915/dsb: Pre allocate and late cleanup of cmd buffer")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Animesh Manna <animesh.manna at intel.com>
> Cc: Uma Shankar <uma.shankar at intel.com>

Thanks Chris for catching.
Reviewed-by: Animesh Manna <animesh.manna at intel.com>

> ---
>   drivers/gpu/drm/i915/display/intel_dsb.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
> index 475106e91fa7..24e6d63e2d47 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -169,15 +169,17 @@ void intel_dsb_indexed_reg_write(const struct intel_crtc_state *crtc_state,
>   void intel_dsb_reg_write(const struct intel_crtc_state *crtc_state,
>   			 i915_reg_t reg, u32 val)
>   {
> -	struct intel_dsb *dsb = crtc_state->dsb;
>   	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
>   	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> -	u32 *buf = dsb->cmd_buf;
> +	struct intel_dsb *dsb;
> +	u32 *buf;
>   
> +	dsb = crtc_state->dsb;
>   	if (!dsb) {
>   		intel_de_write(dev_priv, reg, val);
>   		return;
>   	}
> +
>   	buf = dsb->cmd_buf;
>   	if (drm_WARN_ON(&dev_priv->drm, dsb->free_pos >= DSB_BUF_SIZE)) {
>   		drm_dbg_kms(&dev_priv->drm, "DSB buffer overflow\n");