[PATCH 7/8] drm: Split connection_mutex out of mode_config.mutex (v2)

[Rob Clark <robdclark@gmail.com>]

From: Daniel Vetter <daniel.vetter@ffwll.ch>

After the split-out of crtc locks from the big mode_config.mutex
there's still two major areas it protects:
- Various connector probe states, like connector->status, EDID
  properties, probed mode lists and similar information.
- The links from connector->encoder and encoder->crtc and other
  modeset-relevant connector state (e.g. properties which control the
  panel fitter).

The later is used by modeset operations. But they don't really care
about the former since it's allowed to e.g. enable a disconnected VGA
output or with a mode not in the probed list.

Thus far this hasn't been a problem, but for the atomic modeset
conversion Rob Clark needs to convert all modeset relevant locks into
w/w locks. This is required because the order of acquisition is
determined by how userspace supplies the atomic modeset data. This has
run into troubles in the detect path since the i915 load detect code
needs _both_ protections offered by the mode_config.mutex: It updates
probe state and it needs to change the modeset configuration to enable
the temporary load detect pipe.

The big deal here is that for the probe/detect users of this lock a
plain mutex fits best, but for atomic modesets we really want a w/w
mutex. To fix this lets split out a new connection_mutex lock for the
modeset relevant parts.

For simplicity I've decided to only add one additional lock for all
connector/encoder links and modeset configuration states. We have
piles of different modeset objects in addition to those (like bridges
or panels), so adding per-object locks would be much more effort.

Also, we're guaranteed (at least for now) to do a full modeset if we
need to acquire this lock. Which means that fine-grained locking is
fairly irrelevant compared to the amount of time the full modeset will
take.

I've done a full audit, and there's just a few things that justify
special focus:
- Locking in drm_sysfs.c is almost completely absent. We should
  sprinkle mode_config.connection_mutex over this file a bit, but
  since it already lacks mode_config.mutex this patch wont make the
  situation any worse. This is material for a follow-up patch.

- omap has a omap_framebuffer_flush function which walks the
  connector->encoder->crtc links and is called from many contexts.
  Some look like they don't acquire mode_config.mutex, so this is
  already racy. Again fixing this is material for a separate patch.

- The radeon hot_plug function to retrain DP links looks at
  connector->dpms. Currently this happens without any locking, so is
  already racy. I think radeon_hotplug_work_func should gain
  mutex_lock/unlock calls for the mode_config.connection_mutex.

- Same applies to i915's intel_dp_hot_plug. But again, this is already
  racy.

- i915 load_detect code needs to acquire this lock. Which means the
  w/w dance due to Rob's work will be nicely contained to _just_ this
  function.

I've added fixme comments everywhere where it looks suspicious but in
the sysfs code. After a quick irc discussion with Dave Airlie it
sounds like the lack of locking in there is due to sysfs cleanup fun
at module unload.

v1: original (only compile tested)
v2: missing mutex_init(), etc

Cc: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rob Clark <robdclark@gmail.com>
---
 drivers/gpu/drm/drm_crtc.c                 | 8 ++++++++
 drivers/gpu/drm/drm_crtc_helper.c          | 2 ++
 drivers/gpu/drm/drm_edid.c                 | 2 ++
 drivers/gpu/drm/drm_plane_helper.c         | 7 +++++++
 drivers/gpu/drm/i915/intel_display.c       | 9 ++++++++-
 drivers/gpu/drm/i915/intel_dp.c            | 1 +
 drivers/gpu/drm/omapdrm/omap_fb.c          | 1 +
 drivers/gpu/drm/radeon/radeon_connectors.c | 1 +
 include/drm/drm_crtc.h                     | 1 +
 9 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 4d243fd..de1520c 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -54,6 +54,8 @@ void drm_modeset_lock_all(struct drm_device *dev)
 
 	mutex_lock(&dev->mode_config.mutex);
 
+	mutex_lock(&dev->mode_config.connection_mutex);
+
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
 		mutex_lock_nest_lock(&crtc->mutex, &dev->mode_config.mutex);
 }
@@ -72,6 +74,8 @@ void drm_modeset_unlock_all(struct drm_device *dev)
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
 		mutex_unlock(&crtc->mutex);
 
+	mutex_unlock(&dev->mode_config.connection_mutex);
+
 	mutex_unlock(&dev->mode_config.mutex);
 }
 EXPORT_SYMBOL(drm_modeset_unlock_all);
@@ -93,6 +97,7 @@ void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
 		WARN_ON(!mutex_is_locked(&crtc->mutex));
 
+	WARN_ON(!mutex_is_locked(&dev->mode_config.connection_mutex));
 	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
 }
 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
@@ -1799,6 +1804,7 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	DRM_DEBUG_KMS("[CONNECTOR:%d:?]\n", out_resp->connector_id);
 
 	mutex_lock(&dev->mode_config.mutex);
+	mutex_lock(&dev->mode_config.connection_mutex);
 
 	connector = drm_connector_find(dev, out_resp->connector_id);
 	if (!connector) {
@@ -1897,6 +1903,7 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 	out_resp->count_encoders = encoders_count;
 
 out:
+	mutex_unlock(&dev->mode_config.connection_mutex);
 	mutex_unlock(&dev->mode_config.mutex);
 
 	return ret;
@@ -4637,6 +4644,7 @@ EXPORT_SYMBOL(drm_format_vert_chroma_subsampling);
 void drm_mode_config_init(struct drm_device *dev)
 {
 	mutex_init(&dev->mode_config.mutex);
+	mutex_init(&dev->mode_config.connection_mutex);
 	mutex_init(&dev->mode_config.idr_mutex);
 	mutex_init(&dev->mode_config.fb_lock);
 	INIT_LIST_HEAD(&dev->mode_config.fb_list);
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 54e8fdb..5b93caf 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -89,6 +89,8 @@ bool drm_helper_encoder_in_use(struct drm_encoder *encoder)
 	struct drm_device *dev = encoder->dev;
 
 	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+	WARN_ON(!mutex_is_locked(&dev->mode_config.connection_mutex));
+
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head)
 		if (connector->encoder == encoder)
 			return true;
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index d74239f..e3bc051 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -3299,6 +3299,8 @@ struct drm_connector *drm_select_eld(struct drm_encoder *encoder,
 	struct drm_connector *connector;
 	struct drm_device *dev = encoder->dev;
 
+	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head)
 		if (connector->encoder == encoder && connector->eld[0])
 			return connector;
diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index d966afa..458d9bf 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -54,6 +54,13 @@ static int get_connectors_for_crtc(struct drm_crtc *crtc,
 	struct drm_connector *connector;
 	int count = 0;
 
+	/*
+	 * Note: Once we change the plane hooks to more fine-grained locking we
+	 * need to grab the connection_mutex here to be able to make these
+	 * checks.
+	 */
+	WARN_ON(!mutex_is_locked(&dev->mode_config.connection_mutex));
+
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head)
 		if (connector->encoder && connector->encoder->crtc == crtc) {
 			if (connector_list != NULL && count < num_connectors)
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 72b5c34..5844f07 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7988,6 +7988,8 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
 		      connector->base.id, drm_get_connector_name(connector),
 		      encoder->base.id, drm_get_encoder_name(encoder));
 
+	mutex_lock(&dev->mode_config.connection_mutex);
+
 	/*
 	 * Algorithm gets a little messy:
 	 *
@@ -8030,7 +8032,7 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
 	 */
 	if (!crtc) {
 		DRM_DEBUG_KMS("no pipe available for load-detect\n");
-		return false;
+		goto fail_unlock_connector;
 	}
 
 	mutex_lock(&crtc->mutex);
@@ -8084,6 +8086,9 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
 	else
 		intel_crtc->new_config = NULL;
 	mutex_unlock(&crtc->mutex);
+fail_unlock_connector:
+	mutex_unlock(&dev->mode_config.connection_mutex);
+
 	return false;
 }
 
@@ -8113,6 +8118,7 @@ void intel_release_load_detect_pipe(struct drm_connector *connector,
 		}
 
 		mutex_unlock(&crtc->mutex);
+		mutex_unlock(&connector->dev->mode_config.connection_mutex);
 		return;
 	}
 
@@ -8121,6 +8127,7 @@ void intel_release_load_detect_pipe(struct drm_connector *connector,
 		connector->funcs->dpms(connector, old->dpms_mode);
 
 	mutex_unlock(&crtc->mutex);
+	mutex_unlock(&connector->dev->mode_config.connection_mutex);
 }
 
 static int i9xx_pll_refclk(struct drm_device *dev,
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 34ed143..ce52045 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2953,6 +2953,7 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 	u8 sink_irq_vector;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 
+	/* FIXME: This access isn't protected by any locks. */
 	if (!intel_encoder->connectors_active)
 		return;
 
diff --git a/drivers/gpu/drm/omapdrm/omap_fb.c b/drivers/gpu/drm/omapdrm/omap_fb.c
index 8b01960..2a5cacd 100644
--- a/drivers/gpu/drm/omapdrm/omap_fb.c
+++ b/drivers/gpu/drm/omapdrm/omap_fb.c
@@ -346,6 +346,7 @@ void omap_framebuffer_flush(struct drm_framebuffer *fb,
 
 	VERB("flush: %d,%d %dx%d, fb=%p", x, y, w, h, fb);
 
+	/* FIXME: This is racy - no protection against modeset config changes. */
 	while ((connector = omap_framebuffer_get_next_connector(fb, connector))) {
 		/* only consider connectors that are part of a chain */
 		if (connector->encoder && connector->encoder->crtc) {
diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index ea50e0a..bcfe5d5 100644
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -48,6 +48,7 @@ void radeon_connector_hotplug(struct drm_connector *connector)
 	radeon_hpd_set_polarity(rdev, radeon_connector->hpd.hpd);
 
 	/* if the connector is already off, don't turn it back on */
+	/* FIXME: This access isn't protected by any locks. */
 	if (connector->dpms != DRM_MODE_DPMS_ON)
 		return;
 
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 44d7964..1bd6708 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -738,6 +738,7 @@ struct drm_mode_group {
  */
 struct drm_mode_config {
 	struct mutex mutex; /* protects configuration (mode lists etc.) */
+	struct mutex connection_mutex; /* protects connector->encoder and encoder->crtc links */
 	struct mutex idr_mutex; /* for IDR management */
 	struct idr crtc_idr; /* use this idr for all IDs, fb, crtc, connector, modes - just makes life easier */
 	/* this is limited to one for now */
-- 
1.9.3