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Message-ID: <ac1abf6b0e525160b91b75042b678c515b5780cd.camel@redhat.com>
Date: Mon, 14 Nov 2022 16:24:38 -0500
From: Lyude Paul <lyude@...hat.com>
To: "Lin, Wayne" <Wayne.Lin@....com>,
"amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>
Cc: "Wentland, Harry" <Harry.Wentland@....com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>,
"Li, Sun peng (Leo)" <Sunpeng.Li@....com>,
"Siqueira, Rodrigo" <Rodrigo.Siqueira@....com>,
"Deucher, Alexander" <Alexander.Deucher@....com>,
"Koenig, Christian" <Christian.Koenig@....com>,
"Pan, Xinhui" <Xinhui.Pan@....com>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
"Kazlauskas, Nicholas" <Nicholas.Kazlauskas@....com>,
"Pillai, Aurabindo" <Aurabindo.Pillai@....com>,
"Li, Roman" <Roman.Li@....com>, "Zuo, Jerry" <Jerry.Zuo@....com>,
"Wu, Hersen" <hersenxs.wu@....com>,
Thomas Zimmermann <tzimmermann@...e.de>,
"Mahfooz, Hamza" <Hamza.Mahfooz@....com>,
"Hung, Alex" <Alex.Hung@....com>,
"Francis, David" <David.Francis@....com>,
Mikita Lipski <mikita.lipski@....com>,
"Liu, Wenjing" <Wenjing.Liu@....com>,
"open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and
deadlocking
On Wed, 2022-11-09 at 09:48 +0000, Lin, Wayne wrote:
> [Public]
>
> Thanks, Lyude!
> Comments inline.
>
> > -----Original Message-----
> > From: Lyude Paul <lyude@...hat.com>
> > Sent: Saturday, November 5, 2022 7:59 AM
> > To: amd-gfx@...ts.freedesktop.org
> > Cc: Wentland, Harry <Harry.Wentland@....com>; stable@...r.kernel.org;
> > Li, Sun peng (Leo) <Sunpeng.Li@....com>; Siqueira, Rodrigo
> > <Rodrigo.Siqueira@....com>; Deucher, Alexander
> > <Alexander.Deucher@....com>; Koenig, Christian
> > <Christian.Koenig@....com>; Pan, Xinhui <Xinhui.Pan@....com>; David
> > Airlie <airlied@...il.com>; Daniel Vetter <daniel@...ll.ch>; Kazlauskas,
> > Nicholas <Nicholas.Kazlauskas@....com>; Pillai, Aurabindo
> > <Aurabindo.Pillai@....com>; Li, Roman <Roman.Li@....com>; Zuo, Jerry
> > <Jerry.Zuo@....com>; Wu, Hersen <hersenxs.wu@....com>; Lin, Wayne
> > <Wayne.Lin@....com>; Thomas Zimmermann <tzimmermann@...e.de>;
> > Mahfooz, Hamza <Hamza.Mahfooz@....com>; Hung, Alex
> > <Alex.Hung@....com>; Francis, David <David.Francis@....com>; Mikita
> > Lipski <mikita.lipski@....com>; Liu, Wenjing <Wenjing.Liu@....com>;
> > open list:DRM DRIVERS <dri-devel@...ts.freedesktop.org>; open list <linux-
> > kernel@...r.kernel.org>
> > Subject: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and
> > deadlocking
> >
> > It appears that amdgpu makes the mistake of completely ignoring the return
> > values from the DP MST helpers, and instead just returns a simple true/false.
> > In this case, it seems to have come back to bite us because as a result of
> > simply returning false from compute_mst_dsc_configs_for_state(), amdgpu
> > had no way of telling when a deadlock happened from these helpers. This
> > could definitely result in some kernel splats.
> >
> > Signed-off-by: Lyude Paul <lyude@...hat.com>
> > Fixes: 8c20a1ed9b4f ("drm/amd/display: MST DSC compute fair share")
> > Cc: Harry Wentland <harry.wentland@....com>
> > Cc: <stable@...r.kernel.org> # v5.6+
> > ---
> > .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 18 +--
> > .../display/amdgpu_dm/amdgpu_dm_mst_types.c | 107 ++++++++++------
> > --
> > .../display/amdgpu_dm/amdgpu_dm_mst_types.h | 12 +-
> > 3 files changed, 73 insertions(+), 64 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > index 0db2a88cd4d7b..6f76b2c84cdb5 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -6462,7 +6462,7 @@ static int
> > dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
> > struct drm_connector_state *new_con_state;
> > struct amdgpu_dm_connector *aconnector;
> > struct dm_connector_state *dm_conn_state;
> > - int i, j;
> > + int i, j, ret;
> > int vcpi, pbn_div, pbn, slot_num = 0;
> >
> > for_each_new_connector_in_state(state, connector,
> > new_con_state, i) { @@ -6509,8 +6509,11 @@ static int
> > dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
> > dm_conn_state->pbn = pbn;
> > dm_conn_state->vcpi_slots = slot_num;
> >
> > - drm_dp_mst_atomic_enable_dsc(state, aconnector-
> > > port, dm_conn_state->pbn,
> > - false);
> > + ret = drm_dp_mst_atomic_enable_dsc(state,
> > aconnector->port,
> > + dm_conn_state-
> > > pbn, false);
> > + if (ret != 0)
> > + return ret;
> > +
> > continue;
> > }
> >
> > @@ -9523,10 +9526,9 @@ static int amdgpu_dm_atomic_check(struct
> > drm_device *dev,
> >
> > #if defined(CONFIG_DRM_AMD_DC_DCN)
> > if (dc_resource_is_dsc_encoding_supported(dc)) {
> > - if (!pre_validate_dsc(state, &dm_state, vars)) {
> > - ret = -EINVAL;
> > + ret = pre_validate_dsc(state, &dm_state, vars);
> > + if (ret != 0)
> > goto fail;
> > - }
> > }
> > #endif
> >
> > @@ -9621,9 +9623,9 @@ static int amdgpu_dm_atomic_check(struct
> > drm_device *dev,
> > }
> >
> > #if defined(CONFIG_DRM_AMD_DC_DCN)
> > - if (!compute_mst_dsc_configs_for_state(state, dm_state-
> > > context, vars)) {
> > + ret = compute_mst_dsc_configs_for_state(state, dm_state-
> > > context, vars);
> > + if (ret) {
> >
> > DRM_DEBUG_DRIVER("compute_mst_dsc_configs_for_state()
> > failed\n");
> > - ret = -EINVAL;
> > goto fail;
> > }
> >
> > diff --git
> > a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> > index 6ff96b4bdda5c..30bc2e5058b70 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> > +++
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> > @@ -864,25 +864,25 @@ static bool try_disable_dsc(struct
> > drm_atomic_state *state,
> > return true;
> > }
> >
> > -static bool compute_mst_dsc_configs_for_link(struct drm_atomic_state
> > *state,
> > - struct dc_state *dc_state,
> > - struct dc_link *dc_link,
> > - struct dsc_mst_fairness_vars *vars,
> > - struct drm_dp_mst_topology_mgr
> > *mgr,
> > - int *link_vars_start_index)
> > +static int compute_mst_dsc_configs_for_link(struct drm_atomic_state
> > *state,
> > + struct dc_state *dc_state,
> > + struct dc_link *dc_link,
> > + struct dsc_mst_fairness_vars *vars,
> > + struct drm_dp_mst_topology_mgr
> > *mgr,
> > + int *link_vars_start_index)
> > {
> > struct dc_stream_state *stream;
> > struct dsc_mst_fairness_params params[MAX_PIPES];
> > struct amdgpu_dm_connector *aconnector;
> > struct drm_dp_mst_topology_state *mst_state =
> > drm_atomic_get_mst_topology_state(state, mgr);
> > int count = 0;
> > - int i, k;
> > + int i, k, ret;
> > bool debugfs_overwrite = false;
> >
> > memset(params, 0, sizeof(params));
> >
> > if (IS_ERR(mst_state))
> > - return false;
> > + return PTR_ERR(mst_state);
> >
> > mst_state->pbn_div = dm_mst_get_pbn_divider(dc_link); #if
> > defined(CONFIG_DRM_AMD_DC_DCN) @@ -933,7 +933,7 @@ static bool
> > compute_mst_dsc_configs_for_link(struct drm_atomic_state *state,
> >
> > if (count == 0) {
> > ASSERT(0);
> > - return true;
> > + return 0;
> > }
> >
> > /* k is start index of vars for current phy link used by mst hub */ @@
> > -949,11 +949,14 @@ static bool compute_mst_dsc_configs_for_link(struct
> > drm_atomic_state *state,
> > vars[i + k].bpp_x16 = 0;
> > if (drm_dp_atomic_find_time_slots(state, params[i].port-
> > > mgr, params[i].port,
> > vars[i + k].pbn) < 0)
> > - return false;
> > + return -EINVAL;
>
> Should we also return the error code get from drm_dp_atomic_find_time_slots() rather than
> assigning a new one here?
Yes we should, nice catch!
>
> > }
> > - if (!drm_dp_mst_atomic_check(state) && !debugfs_overwrite) {
> > + ret = drm_dp_mst_atomic_check(state);
> > + if (ret == 0 && !debugfs_overwrite) {
> > set_dsc_configs_from_fairness_vars(params, vars, count, k);
> > - return true;
> > + return 0;
> > + } else if (ret == -EDEADLK) {
> > + return ret;
>
> I think we should return here whenever there is an error. Not just for EDEADLK case.
sgtm
>
> > }
> >
> > /* Try max compression */
> > @@ -964,29 +967,30 @@ static bool
> > compute_mst_dsc_configs_for_link(struct drm_atomic_state *state,
> > vars[i + k].bpp_x16 =
> > params[i].bw_range.min_target_bpp_x16;
> > if (drm_dp_atomic_find_time_slots(state,
> > params[i].port->mgr,
> > params[i].port, vars[i
> > + k].pbn) < 0)
> > - return false;
> > + return -EINVAL;
>
> Same as above.
>
> > } else {
> > vars[i + k].pbn =
> > kbps_to_peak_pbn(params[i].bw_range.stream_kbps);
> > vars[i + k].dsc_enabled = false;
> > vars[i + k].bpp_x16 = 0;
> > if (drm_dp_atomic_find_time_slots(state,
> > params[i].port->mgr,
> > params[i].port, vars[i
> > + k].pbn) < 0)
> > - return false;
> > + return -EINVAL;
>
> Same as above.
>
> > }
> > }
> > - if (drm_dp_mst_atomic_check(state))
> > - return false;
> > + ret = drm_dp_mst_atomic_check(state);
> > + if (ret != 0)
> > + return ret;
> >
> > /* Optimize degree of compression */
> > if (!increase_dsc_bpp(state, mst_state, dc_link, params, vars, count,
> > k))
> > - return false;
> > + return -ENOSPC;
> >
> > if (!try_disable_dsc(state, dc_link, params, vars, count, k))
> > - return false;
> > + return -ENOSPC;
> >
> > set_dsc_configs_from_fairness_vars(params, vars, count, k);
> >
> > - return true;
> > + return 0;
> > }
> >
> > static bool is_dsc_need_re_compute(
> > @@ -1087,15 +1091,16 @@ static bool is_dsc_need_re_compute(
> > return is_dsc_need_re_compute;
> > }
> >
> > -bool compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> > - struct dc_state *dc_state,
> > - struct dsc_mst_fairness_vars *vars)
> > +int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> > + struct dc_state *dc_state,
> > + struct dsc_mst_fairness_vars *vars)
> > {
> > int i, j;
> > struct dc_stream_state *stream;
> > bool computed_streams[MAX_PIPES];
> > struct amdgpu_dm_connector *aconnector;
> > int link_vars_start_index = 0;
> > + int ret = 0;
> >
> > for (i = 0; i < dc_state->stream_count; i++)
> > computed_streams[i] = false;
> > @@ -1118,17 +1123,19 @@ bool compute_mst_dsc_configs_for_state(struct
> > drm_atomic_state *state,
> > continue;
> >
> > if (dcn20_remove_stream_from_ctx(stream->ctx->dc,
> > dc_state, stream) != DC_OK)
> > - return false;
> > + return -EINVAL;
> >
> > if (!is_dsc_need_re_compute(state, dc_state, stream->link))
> > continue;
> >
> > mutex_lock(&aconnector->mst_mgr.lock);
> > - if (!compute_mst_dsc_configs_for_link(state, dc_state,
> > stream->link, vars,
> > - &aconnector->mst_mgr,
> > - &link_vars_start_index)) {
> > +
> > + ret = compute_mst_dsc_configs_for_link(state, dc_state,
> > stream->link, vars,
> > + &aconnector->mst_mgr,
> > + &link_vars_start_index);
> > + if (ret != 0) {
> > mutex_unlock(&aconnector->mst_mgr.lock);
> > - return false;
> > + return ret;
> > }
> > mutex_unlock(&aconnector->mst_mgr.lock);
> >
> > @@ -1143,22 +1150,22 @@ bool compute_mst_dsc_configs_for_state(struct
> > drm_atomic_state *state,
> >
> > if (stream->timing.flags.DSC == 1)
> > if (dc_stream_add_dsc_to_resource(stream->ctx-
> > > dc, dc_state, stream) != DC_OK)
> > - return false;
> > + return -EINVAL;
> > }
> >
> > - return true;
> > + return ret;
> > }
> >
> > -static bool
> > - pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state
> > *state,
> > - struct dc_state *dc_state,
> > - struct dsc_mst_fairness_vars
> > *vars)
> > +static int pre_compute_mst_dsc_configs_for_state(struct
> > drm_atomic_state *state,
> > + struct dc_state *dc_state,
> > + struct dsc_mst_fairness_vars
> > *vars)
> > {
> > int i, j;
> > struct dc_stream_state *stream;
> > bool computed_streams[MAX_PIPES];
> > struct amdgpu_dm_connector *aconnector;
> > int link_vars_start_index = 0;
> > + int ret;
> >
> > for (i = 0; i < dc_state->stream_count; i++)
> > computed_streams[i] = false;
> > @@ -1184,13 +1191,12 @@ static bool
> > continue;
> >
> > mutex_lock(&aconnector->mst_mgr.lock);
> > - if (!compute_mst_dsc_configs_for_link(state, dc_state,
> > stream->link, vars,
> > - &aconnector->mst_mgr,
> > - &link_vars_start_index)) {
> > - mutex_unlock(&aconnector->mst_mgr.lock);
> > - return false;
> > - }
> > + ret = compute_mst_dsc_configs_for_link(state, dc_state,
> > stream->link, vars,
> > + &aconnector->mst_mgr,
> > + &link_vars_start_index);
> > mutex_unlock(&aconnector->mst_mgr.lock);
> > + if (ret != 0)
> > + return ret;
> >
> > for (j = 0; j < dc_state->stream_count; j++) {
> > if (dc_state->streams[j]->link == stream->link) @@ -
> > 1198,7 +1204,7 @@ static bool
> > }
> > }
> >
> > - return true;
> > + return ret;
> > }
> >
> > static int find_crtc_index_in_state_by_stream(struct drm_atomic_state
> > *state, @@ -1253,9 +1259,9 @@ static bool
> > is_dsc_precompute_needed(struct drm_atomic_state *state)
> > return ret;
> > }
> >
> > -bool pre_validate_dsc(struct drm_atomic_state *state,
> > - struct dm_atomic_state **dm_state_ptr,
> > - struct dsc_mst_fairness_vars *vars)
> > +int pre_validate_dsc(struct drm_atomic_state *state,
> > + struct dm_atomic_state **dm_state_ptr,
> > + struct dsc_mst_fairness_vars *vars)
> > {
> > int i;
> > struct dm_atomic_state *dm_state;
> > @@ -1264,11 +1270,12 @@ bool pre_validate_dsc(struct drm_atomic_state
> > *state,
> >
> > if (!is_dsc_precompute_needed(state)) {
> > DRM_INFO_ONCE("DSC precompute is not needed.\n");
> > - return true;
> > + return 0;
> > }
> > - if (dm_atomic_get_state(state, dm_state_ptr)) {
> > + ret = dm_atomic_get_state(state, dm_state_ptr);
> > + if (ret != 0) {
> > DRM_INFO_ONCE("dm_atomic_get_state() failed\n");
> > - return false;
> > + return ret;
> > }
> > dm_state = *dm_state_ptr;
> >
> > @@ -1280,7 +1287,7 @@ bool pre_validate_dsc(struct drm_atomic_state
> > *state,
> >
> > local_dc_state = kmemdup(dm_state->context, sizeof(struct
> > dc_state), GFP_KERNEL);
> > if (!local_dc_state)
> > - return false;
> > + return -ENOMEM;
> >
> > for (i = 0; i < local_dc_state->stream_count; i++) {
> > struct dc_stream_state *stream = dm_state->context-
> > > streams[i]; @@ -1316,9 +1323,9 @@ bool pre_validate_dsc(struct
> > drm_atomic_state *state,
> > if (ret != 0)
> > goto clean_exit;
> >
> > - if (!pre_compute_mst_dsc_configs_for_state(state, local_dc_state,
> > vars)) {
> > + ret = pre_compute_mst_dsc_configs_for_state(state, local_dc_state,
> > vars);
> > + if (ret != 0) {
> >
> > DRM_INFO_ONCE("pre_compute_mst_dsc_configs_for_state()
> > failed\n");
> > - ret = -EINVAL;
> > goto clean_exit;
> > }
> >
> > @@ -1349,7 +1356,7 @@ bool pre_validate_dsc(struct drm_atomic_state
> > *state,
> >
> > kfree(local_dc_state);
> >
> > - return (ret == 0);
> > + return ret;
> > }
> >
> > static unsigned int kbps_from_pbn(unsigned int pbn) diff --git
> > a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> > index b92a7c5671aa2..97fd70df531bf 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> > +++
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> > @@ -53,15 +53,15 @@ struct dsc_mst_fairness_vars {
> > struct amdgpu_dm_connector *aconnector; };
> >
> > -bool compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> > - struct dc_state *dc_state,
> > - struct dsc_mst_fairness_vars *vars);
> > +int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> > + struct dc_state *dc_state,
> > + struct dsc_mst_fairness_vars *vars);
> >
> > bool needs_dsc_aux_workaround(struct dc_link *link);
> >
> > -bool pre_validate_dsc(struct drm_atomic_state *state,
> > - struct dm_atomic_state **dm_state_ptr,
> > - struct dsc_mst_fairness_vars *vars);
> > +int pre_validate_dsc(struct drm_atomic_state *state,
> > + struct dm_atomic_state **dm_state_ptr,
> > + struct dsc_mst_fairness_vars *vars);
> >
> > enum dc_status dm_dp_mst_is_port_support_mode(
> > struct amdgpu_dm_connector *aconnector,
> > --
> > 2.37.3
> ---
> Regards,
> Wayne Lin
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
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