Re: [Intel-gfx] [PATCH] drm/atomic-helpers: remove legacy_cursor_update hacks

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi Daniel

Am 31.03.22 um 17:20 schrieb Daniel Vetter:
> The stuff never really worked, and leads to lots of fun because it
> out-of-order frees atomic states. Which upsets KASAN, among other
> things.
> 
> For async updates we now have a more solid solution with the
> ->atomic_async_check and ->atomic_async_commit hooks. Support for that
> for msm and vc4 landed. nouveau and i915 have their own commit
> routines, doing something similar.
> 
> For everyone else it's probably better to remove the use-after-free
> bug, and encourage folks to use the async support instead. The
> affected drivers which register a legacy cursor plane and don't either
> use the new async stuff or their own commit routine are: amdgpu,
> atmel, mediatek, qxl, rockchip, sti, sun4i, tegra, virtio, and vmwgfx.

A while ago, I received a patch for a bug in ast. Cursor movement 
interfered with modesetting. [1] I didn't really knew what to make of 
it. Could this be related to the problem you're describing here?

I guess the correct fix would be to implement async operations for 
cursor planes? ast doesn't do this yet.

Best regards
Thomas

[1] 
https://lore.kernel.org/dri-devel/20210917072226.17357-1-kuohsiang_chou@aspeedtech.com/

> 
> Inspired by an amdgpu bug report.
> 
> v2: Drop RFC, I think with amdgpu converted over to use
> atomic_async_check/commit done in
> 
> commit 674e78acae0dfb4beb56132e41cbae5b60f7d662
> Author: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
> Date:   Wed Dec 5 14:59:07 2018 -0500
> 
>      drm/amd/display: Add fast path for cursor plane updates
> 
> we don't have any driver anymore where we have userspace expecting
> solid legacy cursor support _and_ they are using the atomic helpers in
> their fully glory. So we can retire this.
> 
> v3: Paper over msm and i915 regression. The complete_all is the only
> thing missing afaict.
> 
> v4: Fixup i915 fixup ...
> 
> References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> References: https://lore.kernel.org/all/20220221134155.125447-9-maxime@cerno.tech/
> References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> Cc: Maxime Ripard <maxime@cerno.tech>
> Tested-by: Maxime Ripard <maxime@cerno.tech>
> Cc: mikita.lipski@amd.com
> Cc: Michel Dänzer <michel@daenzer.net>
> Cc: harry.wentland@amd.com
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: "Kazlauskas, Nicholas" <nicholas.kazlauskas@amd.com>
> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>   drivers/gpu/drm/drm_atomic_helper.c          | 13 -------------
>   drivers/gpu/drm/i915/display/intel_display.c | 14 ++++++++++++++
>   drivers/gpu/drm/msm/msm_atomic.c             |  2 ++
>   3 files changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 9603193d2fa1..a2899af82b4a 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1498,13 +1498,6 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
>   	int i, ret;
>   	unsigned int crtc_mask = 0;
>   
> -	 /*
> -	  * Legacy cursor ioctls are completely unsynced, and userspace
> -	  * relies on that (by doing tons of cursor updates).
> -	  */
> -	if (old_state->legacy_cursor_update)
> -		return;
> -
>   	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>   		if (!new_crtc_state->active)
>   			continue;
> @@ -2135,12 +2128,6 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
>   			continue;
>   		}
>   
> -		/* Legacy cursor updates are fully unsynced. */
> -		if (state->legacy_cursor_update) {
> -			complete_all(&commit->flip_done);
> -			continue;
> -		}
> -
>   		if (!new_crtc_state->event) {
>   			commit->event = kzalloc(sizeof(*commit->event),
>   						GFP_KERNEL);
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index d2abe0e430bf..6ca5a6e7703b 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -8799,6 +8799,20 @@ static int intel_atomic_commit(struct drm_device *dev,
>   		intel_runtime_pm_put(&dev_priv->runtime_pm, state->wakeref);
>   		return ret;
>   	}
> +
> +	/*
> +	 * FIXME: Cut over to (async) commit helpers instead of hand-rolling
> +	 * everything.
> +	 */
> +	if (state->base.legacy_cursor_update) {
> +		struct intel_crtc_state *new_crtc_state;
> +		struct intel_crtc *crtc;
> +		int i;
> +
> +		for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i)
> +			complete_all(&new_crtc_state->uapi.commit->flip_done);
> +	}
> +
>   	intel_shared_dpll_swap_state(state);
>   	intel_atomic_track_fbs(state);
>   
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
> index 1686fbb611fd..b3cfabebe5d6 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -222,6 +222,8 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
>   		/* async updates are limited to single-crtc updates: */
>   		WARN_ON(crtc_mask != drm_crtc_mask(async_crtc));
>   
> +		complete_all(&async_crtc->state->commit->flip_done);
> +
>   		/*
>   		 * Start timer if we don't already have an update pending
>   		 * on this crtc:

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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