[PATCH] drm/atomic-helpers: remove legacy_cursor_update hacks - dri-devel - freedesktop.org experimental mailing list

31 Mar 2022

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.
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:
-- 
2.34.1


    