linux-kernel - Re: [PATCH] drm/amd/display: prevent potential division by zero errors

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Message-ID: <e523a175-9f83-492e-996c-4a1fc0622149@amd.com>
Date:   Tue, 5 Sep 2023 15:28:00 -0400
From:   Aurabindo Pillai <aurabindo.pillai@....com>
To:     Hamza Mahfooz <hamza.mahfooz@....com>,
        amd-gfx@...ts.freedesktop.org
Cc:     stable@...r.kernel.org, Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Tom Rix <trix@...hat.com>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        Aric Cyr <aric.cyr@....com>,
        Austin Zheng <austin.zheng@....com>,
        Mike Hsieh <Mike.Hsieh@....com>,
        "Leo (Hanghong) Ma" <hanghong.ma@....com>,
        Dillon Varone <Dillon.Varone@....com>,
        Bayan Zabihiyan <bayan.zabihiyan@....com>,
        Amanda Liu <amanda.liu@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: prevent potential division by zero
 errors



On 2023-09-05 14:53, Hamza Mahfooz wrote:
> There are two places in apply_below_the_range() where it's possible for
> a divide by zero error to occur. So, to fix this make sure the divisor
> is non-zero before attempting the computation in both cases.
> 
> Cc: stable@...r.kernel.org
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2637
> Fixes: a463b263032f ("drm/amd/display: Fix frames_to_insert math")
> Fixes: ded6119e825a ("drm/amd/display: Reinstate LFC optimization")
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
> ---
>   drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> index dbd60811f95d..ef3a67409021 100644
> --- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> +++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
> @@ -338,7 +338,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
>   		 *  - Delta for CEIL: delta_from_mid_point_in_us_1
>   		 *  - Delta for FLOOR: delta_from_mid_point_in_us_2
>   		 */
> -		if ((last_render_time_in_us / mid_point_frames_ceil) < in_out_vrr->min_duration_in_us) {
> +		if (mid_point_frames_ceil &&
> +		    (last_render_time_in_us / mid_point_frames_ceil) <
> +		    in_out_vrr->min_duration_in_us) {
>   			/* Check for out of range.
>   			 * If using CEIL produces a value that is out of range,
>   			 * then we are forced to use FLOOR.
> @@ -385,8 +387,9 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
>   		/* Either we've calculated the number of frames to insert,
>   		 * or we need to insert min duration frames
>   		 */
> -		if (last_render_time_in_us / frames_to_insert <
> -				in_out_vrr->min_duration_in_us){
> +		if (frames_to_insert &&
> +		    (last_render_time_in_us / frames_to_insert) <
> +		    in_out_vrr->min_duration_in_us){
>   			frames_to_insert -= (frames_to_insert > 1) ?
>   					1 : 0;
>   		}


Reviewed-by: Aurabindo Pillai <aurabindo.pillai@....com>

--

Thanks & Regards,
Jay