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

From: Rob Clark
Date: Wed Feb 22 2023 - 18:14:45 EST

On Thu, Feb 16, 2023 at 3:12 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
>
> 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@xxxxxxx>
> 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 ...
>
> v5: Unallocate the crtc->event in msm to avoid hitting a WARN_ON in
> dpu_crtc_atomic_flush(). This is a bit a hack, but simplest way to
> untangle this all. Thanks to Abhinav Kumar for the debug help.

Hmm, are you sure about that double-put?

[ +0.501263] ------------[ cut here ]------------
[ +0.000032] refcount_t: underflow; use-after-free.
[ +0.000033] WARNING: CPU: 6 PID: 1854 at lib/refcount.c:28
refcount_warn_saturate+0xf8/0x134
[ +0.000043] Modules linked in: uinput rfcomm algif_hash
algif_skcipher af_alg veth venus_dec venus_enc xt_cgroup xt_MASQUERADE
qcom_spmi_temp_alarm qcom_spmi_adc_tm5 qcom_spmi_adc5 qcom_vadc_common
cros_ec_typec typec 8021q hci_uart btqca qcom_stats venus_core
coresight_etm4x coresight_tmc snd_soc_lpass_sc7180
coresight_replicator coresight_funnel coresight snd_soc_sc7180
ip6table_nat fuse ath10k_snoc ath10k_core ath mac80211 iio_trig_sysfs
bluetooth cros_ec_sensors cfg80211 cros_ec_sensors_core
industrialio_triggered_buffer kfifo_buf ecdh_generic ecc
cros_ec_sensorhub lzo_rle lzo_compress r8153_ecm cdc_ether usbnet
r8152 mii zram hid_vivaldi hid_google_hammer hid_vivaldi_common joydev
[ +0.000189] CPU: 6 PID: 1854 Comm: DrmThread Not tainted
5.15.93-16271-g5ecce40dbcd4 #46
cf9752a1c9e5b13fd13216094f52d77fa5a5f8f3
[ +0.000016] Hardware name: Google Wormdingler rev1+ INX panel board (DT)
[ +0.000008] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ +0.000013] pc : refcount_warn_saturate+0xf8/0x134
[ +0.000011] lr : refcount_warn_saturate+0xf8/0x134
[ +0.000011] sp : ffffffc012e43930
[ +0.000008] x29: ffffffc012e43930 x28: ffffff80d31aa300 x27: 000000000000024e
[ +0.000017] x26: 00000000000003bd x25: 0000000000000040 x24: 0000000000000040
[ +0.000014] x23: ffffff8083eb1000 x22: 0000000000000002 x21: ffffff80845bc800
[ +0.000013] x20: 0000000000000040 x19: ffffff80d0cecb00 x18: 0000000060014024
[ +0.000012] x17: 0000000000000000 x16: 000000000000003c x15: ffffffd97e21a1c0
[ +0.000012] x14: 0000000000000003 x13: 0000000000000004 x12: 0000000000000001
[ +0.000014] x11: c0000000ffffdfff x10: ffffffd97f560f50 x9 : 5749cdb403550d00
[ +0.000014] x8 : 5749cdb403550d00 x7 : 0000000000000000 x6 : 372e31332020205b
[ +0.000012] x5 : ffffffd97f7b8b24 x4 : 0000000000000000 x3 : ffffffc012e43588
[ +0.000013] x2 : ffffffc012e43590 x1 : 00000000ffffdfff x0 : 0000000000000026
[ +0.000014] Call trace:
[ +0.000008] refcount_warn_saturate+0xf8/0x134
[ +0.000013] drm_crtc_commit_put+0x54/0x74
[ +0.000013] __drm_atomic_helper_plane_destroy_state+0x64/0x68
[ +0.000013] dpu_plane_destroy_state+0x24/0x3c
[ +0.000017] drm_atomic_state_default_clear+0x13c/0x2d8
[ +0.000015] __drm_atomic_state_free+0x88/0xa0
[ +0.000015] drm_atomic_helper_update_plane+0x158/0x188
[ +0.000014] __setplane_atomic+0xf4/0x138
[ +0.000012] drm_mode_cursor_common+0x2e8/0x40c
[ +0.000009] drm_mode_cursor_ioctl+0x48/0x70
[ +0.000008] drm_ioctl_kernel+0xe0/0x158
[ +0.000014] drm_ioctl+0x214/0x480
[ +0.000012] __arm64_sys_ioctl+0x94/0xd4
[ +0.000010] invoke_syscall+0x4c/0x100
[ +0.000013] do_el0_svc+0xa4/0x168
[ +0.000012] el0_svc+0x20/0x50
[ +0.000009] el0t_64_sync_handler+0x20/0x110
[ +0.000008] el0t_64_sync+0x1a4/0x1a8
[ +0.000010] ---[ end trace 35bb2d245a684c9a ]---


BR,
-R



> Cc: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Maxime Ripard <maxime@xxxxxxxxxx>
> References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> References: https://lore.kernel.org/all/20220221134155.125447-9-maxime@xxxxxxxxxx/
> References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> Cc: Maxime Ripard <maxime@xxxxxxxxxx>
> Tested-by: Maxime Ripard <maxime@xxxxxxxxxx>
> Cc: mikita.lipski@xxxxxxx
> Cc: Michel Dänzer <michel@xxxxxxxxxxx>
> Cc: harry.wentland@xxxxxxx
> Cc: Rob Clark <robdclark@xxxxxxxxx>
> Cc: "Kazlauskas, Nicholas" <nicholas.kazlauskas@xxxxxxx>
> Cc: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> Cc: Sean Paul <sean@xxxxxxxxxx>
> Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> Cc: "Ville Syrjälä" <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> Cc: Imre Deak <imre.deak@xxxxxxxxx>
> Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> Cc: linux-arm-msm@xxxxxxxxxxxxxxx
> Cc: freedreno@xxxxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-mediatek@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 13 -------------
> drivers/gpu/drm/i915/display/intel_display.c | 14 ++++++++++++++
> drivers/gpu/drm/msm/msm_atomic.c | 15 +++++++++++++++
> 3 files changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index d579fd8f7cb8..f6b4c3a00684 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1587,13 +1587,6 @@ 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;
> @@ -2244,12 +2237,6 @@ 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 3479125fbda6..2454451fcf95 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -7651,6 +7651,20 @@ 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..b7151767b567 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -189,6 +189,19 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
> bool async = kms->funcs->vsync_time &&
> can_do_async(state, &async_crtc);
>
> + /*
> + * FIXME: Convert to async plane helpers and remove the various hacks to
> + * keep the old legacy_cursor_way of doing async commits working for the
> + * dpu code, like the expectation that these don't have a crtc->event.
> + */
> + if (async) {
> + /* both ->event itself and the pointer hold a reference! */
> + drm_crtc_commit_put(async_crtc->state->commit);
> + drm_crtc_commit_put(async_crtc->state->commit);
> + kfree(async_crtc->state->event);
> + async_crtc->state->event = NULL;
> + }
> +
> trace_msm_atomic_commit_tail_start(async, crtc_mask);
>
> kms->funcs->enable_commit(kms);
> @@ -222,6 +235,8 @@ 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:
> --
> 2.39.0
>