linux-kernel - Re: [PATCH v2 1/2] drm/connector: hdmi: Do atomic check when necessary

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Message-ID: <d7bb7ncdljijjdyaqf6tnvs2vk4brrwru2bg5uxmouabdnvocw@kgd63sykbmh4>
Date: Fri, 10 Jan 2025 11:18:35 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Liu Ying <victor.liu@....com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org, 
	Laurent.pinchart@...asonboard.com, jonas@...boo.se, jernej.skrabec@...il.com, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, 
	simona@...ll.ch
Subject: Re: [PATCH v2 1/2] drm/connector: hdmi: Do atomic check when
 necessary

On Fri, Jan 10, 2025 at 04:48:20PM +0800, Liu Ying wrote:
> It's ok to pass atomic check successfully if an atomic commit tries to
> disable the display pipeline which the connector belongs to. That is,
> when the crtc or the best_encoder pointers in struct drm_connector_state
> are NULL, drm_atomic_helper_connector_hdmi_check() should return 0.
> Without the check against the NULL pointers, drm_default_rgb_quant_range()
> called by drm_atomic_helper_connector_hdmi_check() would dereference
> the NULL pointer to_match in drm_match_cea_mode().
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> Call trace:
>  drm_default_rgb_quant_range+0x0/0x4c (P)
>  drm_bridge_connector_atomic_check+0x20/0x2c
>  drm_atomic_helper_check_modeset+0x488/0xc78
>  drm_atomic_helper_check+0x20/0xa4
>  drm_atomic_check_only+0x4b8/0x984
>  drm_atomic_commit+0x48/0xc4
>  drm_framebuffer_remove+0x44c/0x530
>  drm_mode_rmfb_work_fn+0x7c/0xa0
>  process_one_work+0x150/0x294
>  worker_thread+0x2dc/0x3dc
>  kthread+0x130/0x204
>  ret_from_fork+0x10/0x20
> 
> Fixes: 8ec116ff21a9 ("drm/display: bridge_connector: provide atomic_check for HDMI bridges")
> Fixes: 84e541b1e58e ("drm/sun4i: use drm_atomic_helper_connector_hdmi_check()")
> Fixes: 65548c8ff0ab ("drm/rockchip: inno_hdmi: Switch to HDMI connector")
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
> Tested with i.MX8MP imx-lcdif.
> sun4i and rockchip are not tested due to no HW access.
> 
> v2:
> * Trim backtrace in commit message. (Dmitry)
> * Drop timestamps from backtrace commit message. (Dmitry)
> * Move the necessary checks from drm_bridge_connector_atomic_check() to
>   drm_atomic_helper_connector_hdmi_check(). (Dmitry)
> 
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 3 +++
>  1 file changed, 3 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry