When I was writing an atomic wrapper for rmfb, I ran into the
following backtrace from lockdep:
=============================================
[ INFO: possible recursive locking detected ]
4.5.0-patser+ #4696 Tainted: G U
---------------------------------------------
kworker/2:2/2608 is trying to acquire lock:
(crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c9ddc>] drm_modeset_lock+0x7c/0x120 [drm]
but task is already holding lock:
(crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm]
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(crtc_ww_class_mutex);
lock(crtc_ww_class_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
4 locks held by kworker/2:2/2608:
#0: ("events"){.+.+.+}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0
#1: ((&arg.work)){+.+.+.}, at: [<ffffffff810a5eea>] process_one_work+0x15a/0x6c0
#2: (crtc_ww_class_acquire){+.+.+.}, at: [<ffffffffc004532a>] drm_atomic_helper_remove_fb+0x4a/0x1d0 [drm_kms_helper]
#3: (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffc00c98cd>] modeset_backoff+0x8d/0x220 [drm]
While lockdep probably catches this bug when it happens, it's better
to explicitly warn when state->acquire_ctx is not set.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_atomic.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 0b526423f19f..69adcf3944cc 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -263,6 +263,8 @@ drm_atomic_get_crtc_state(struct drm_atomic_state *state,
int ret, index = drm_crtc_index(crtc);
struct drm_crtc_state *crtc_state;
+ WARN_ON(!state->acquire_ctx);
+
crtc_state = drm_atomic_get_existing_crtc_state(state, crtc);
if (crtc_state)
return crtc_state;
@@ -622,6 +624,8 @@ drm_atomic_get_plane_state(struct drm_atomic_state *state,
int ret, index = drm_plane_index(plane);
struct drm_plane_state *plane_state;
+ WARN_ON(!state->acquire_ctx);
+
plane_state = drm_atomic_get_existing_plane_state(state, plane);
if (plane_state)
return plane_state;
@@ -890,6 +894,8 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state,
struct drm_mode_config *config = &connector->dev->mode_config;
struct drm_connector_state *connector_state;
+ WARN_ON(!state->acquire_ctx);
+
ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx);
if (ret)
return ERR_PTR(ret);
--
2.5.5
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