linux-kernel - Re: [PATCH] drm/atomic_helper: Add missing NULL check for drm_plane_helper_funcs.atomic

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Message-ID: <4dc5d357-ffdc-4e91-9519-b23c735c077e@suse.de>
Date: Mon, 30 Sep 2024 08:26:18 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Lyude Paul <lyude@...hat.com>, dri-devel@...ts.freedesktop.org
Cc: stable@...r.kernel.org,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Sean Paul <seanpaul@...omium.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/atomic_helper: Add missing NULL check for
 drm_plane_helper_funcs.atomic_update



Am 27.09.24 um 22:46 schrieb Lyude Paul:
> Something I discovered while writing rvkms since some versions of the
> driver didn't have a filled out atomic_update function - we mention that
> this callback is "optional", but we don't actually check whether it's NULL
> or not before calling it. As a result, we'll segfault if it's not filled
> in.
>
>    rvkms rvkms.0: [drm:drm_atomic_helper_commit_modeset_disables] modeset on [ENCODER:36:Virtual-36]
>    BUG: kernel NULL pointer dereference, address: 0000000000000000
>    PGD 0 P4D 0
>    Oops: Oops: 0010 [#1] PREEMPT SMP NOPTI
>    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240813-1.fc40 08/13/2024
>    RIP: 0010:0x0
>
> So, let's fix that.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Fixes: c2fcd274bce5 ("drm: Add atomic/plane helpers")
> Cc: dri-devel@...ts.freedesktop.org
> Cc: <stable@...r.kernel.org> # v3.19+

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
>   drivers/gpu/drm/drm_atomic_helper.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 43cdf39019a44..b3c507040c6d6 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -2797,7 +2797,8 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev,
>   
>   			funcs->atomic_disable(plane, old_state);
>   		} else if (new_plane_state->crtc || disabling) {
> -			funcs->atomic_update(plane, old_state);
> +			if (funcs->atomic_update)
> +				funcs->atomic_update(plane, old_state);
>   
>   			if (!disabling && funcs->atomic_enable) {
>   				if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
> @@ -2889,7 +2890,8 @@ drm_atomic_helper_commit_planes_on_crtc(struct drm_crtc_state *old_crtc_state)
>   		if (disabling && plane_funcs->atomic_disable) {
>   			plane_funcs->atomic_disable(plane, old_state);
>   		} else if (new_plane_state->crtc || disabling) {
> -			plane_funcs->atomic_update(plane, old_state);
> +			if (plane_funcs->atomic_update)
> +				plane_funcs->atomic_update(plane, old_state);
>   
>   			if (!disabling && plane_funcs->atomic_enable) {
>   				if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
>
> base-commit: 22512c3ee0f47faab5def71c4453638923c62522

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)