linux-kernel - [PATCH v2 4/4] drm/amdgpu/dm/dp_mst: Don't grab mst

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Date:   Mon, 14 Nov 2022 17:17:55 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     amd-gfx@...ts.freedesktop.org
Cc:     stable@...r.kernel.org, Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        hersen wu <hersenxs.wu@....com>,
        Fangzhi Zuo <Jerry.Zuo@....com>, Wayne Lin <Wayne.Lin@....com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Roman Li <Roman.Li@....com>,
        Hamza Mahfooz <hamza.mahfooz@....com>,
        David Francis <David.Francis@....com>,
        Wenjing Liu <Wenjing.Liu@....com>,
        Mikita Lipski <mikita.lipski@....com>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 4/4] drm/amdgpu/dm/dp_mst: Don't grab mst_mgr->lock when computing DSC state

Now that we've fixed the issue with using the incorrect topology manager,
we're actually grabbing the topology manager's lock - and consequently
deadlocking. Luckily for us though, there's actually nothing in AMD's DSC
state computation code that really should need this lock. The one exception
is the mutex_lock() in dm_dp_mst_is_port_support_mode(), however we grab no
locks beneath &mgr->lock there so that should be fine to leave be.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Gitlab issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2171
Fixes: 8c20a1ed9b4f ("drm/amd/display: MST DSC compute fair share")
Cc: <stable@...r.kernel.org> # v5.6+
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 4 ----
 1 file changed, 4 deletions(-)

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 5196c9a0e432d..59648f5ffb59d 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
@@ -1148,10 +1148,8 @@ int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 			continue;
 
 		mst_mgr = aconnector->port->mgr;
-		mutex_lock(&mst_mgr->lock);
 		ret = compute_mst_dsc_configs_for_link(state, dc_state, stream->link, vars, mst_mgr,
 						       &link_vars_start_index);
-		mutex_unlock(&mst_mgr->lock);
 		if (ret != 0)
 			return ret;
 
@@ -1208,10 +1206,8 @@ static int pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
 			continue;
 
 		mst_mgr = aconnector->port->mgr;
-		mutex_lock(&mst_mgr->lock);
 		ret = compute_mst_dsc_configs_for_link(state, dc_state, stream->link, vars, mst_mgr,
 						       &link_vars_start_index);
-		mutex_unlock(&mst_mgr->lock);
 		if (ret != 0)
 			return ret;
 
-- 
2.37.3