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@redhat.com Sent: Saturday, November 5, 2022 7:59 AM To: amd-gfx@lists.freedesktop.org Cc: Wentland, Harry Harry.Wentland@amd.com; stable@vger.kernel.org; Li, Sun peng (Leo) Sunpeng.Li@amd.com; Siqueira, Rodrigo Rodrigo.Siqueira@amd.com; Deucher, Alexander Alexander.Deucher@amd.com; Koenig, Christian Christian.Koenig@amd.com; Pan, Xinhui Xinhui.Pan@amd.com; David Airlie airlied@gmail.com; Daniel Vetter daniel@ffwll.ch; Kazlauskas, Nicholas Nicholas.Kazlauskas@amd.com; Pillai, Aurabindo Aurabindo.Pillai@amd.com; Li, Roman Roman.Li@amd.com; Zuo, Jerry Jerry.Zuo@amd.com; Wu, Hersen hersenxs.wu@amd.com; Lin, Wayne Wayne.Lin@amd.com; Thomas Zimmermann tzimmermann@suse.de; Mahfooz, Hamza Hamza.Mahfooz@amd.com; Hung, Alex Alex.Hung@amd.com; Francis, David David.Francis@amd.com; Mikita Lipski mikita.lipski@amd.com; Liu, Wenjing Wenjing.Liu@amd.com; open list:DRM DRIVERS dri-devel@lists.freedesktop.org; open list <linux- kernel@vger.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@redhat.com Fixes: 8c20a1ed9b4f ("drm/amd/display: MST DSC compute fair share") Cc: Harry Wentland harry.wentland@amd.com Cc: stable@vger.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