drm: rework delayed connector cleanup in connector_iter

PROBE_DEFER also uses system_wq to reprobe drivers, which means when
that again fails, and we try to flush the overall system_wq (to get
all the delayed connectore cleanup work_struct completed), we
deadlock.

Fix this by using just a single cleanup work, so that we can only
flush that one and don't block on anything else. That means a free
list plus locking, a standard pattern.

v2:
- Correctly free connectors only on last ref. Oops (Chris).
- use llist_head/node (Chris).

v3
- Add init_llist_head (Chris).

Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
Cc: Ben Widawsky <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: <[email protected]> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
Cc: <[email protected]> # v4.11+
Cc: Daniel Vetter <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Gustavo Padovan <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Javier Martinez Canillas <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Guillaume Tucker <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: Matt Hart <[email protected]>
Cc: Thierry Escande <[email protected]>
Cc: Tomeu Vizoso <[email protected]>
Cc: Enric Balletbo i Serra <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

2 files changed, 23 insertions, 5 deletions

diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index a4649c56ca2f..5971577016a2 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -24,6 +24,7 @@
 #define __DRM_CONNECTOR_H__
 
 #include <linux/list.h>
+#include <linux/llist.h>
 #include <linux/ctype.h>
 #include <linux/hdmi.h>
 #include <drm/drm_mode_object.h>
@@ -918,12 +919,13 @@ struct drm_connector {
 	uint16_t tile_h_size, tile_v_size;
 
 	/**
-	 * @free_work:
+	 * @free_node:
 	 *
-	 * Work used only by &drm_connector_iter to be able to clean up a
-	 * connector from any context.
+	 * List used only by &drm_connector_iter to be able to clean up a
+	 * connector from any context, in conjunction with
+	 * &drm_mode_config.connector_free_work.
 	 */
-	struct work_struct free_work;
+	struct llist_node free_node;
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index b21e827c5c78..b0ce26d71296 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -27,6 +27,7 @@
 #include <linux/types.h>
 #include <linux/idr.h>
 #include <linux/workqueue.h>
+#include <linux/llist.h>
 
 #include <drm/drm_modeset_lock.h>
 
@@ -393,7 +394,7 @@ struct drm_mode_config {
 
 	/**
 	 * @connector_list_lock: Protects @num_connector and
-	 * @connector_list.
+	 * @connector_list and @connector_free_list.
 	 */
 	spinlock_t connector_list_lock;
 	/**
@@ -414,6 +415,21 @@ struct drm_mode_config {
 	 */
 	struct list_head connector_list;
 	/**
+	 * @connector_free_list:
+	 *
+	 * List of connector objects linked with &drm_connector.free_head.
+	 * Protected by @connector_list_lock. Used by
+	 * drm_for_each_connector_iter() and
+	 * &struct drm_connector_list_iter to savely free connectors using
+	 * @connector_free_work.
+	 */
+	struct llist_head connector_free_list;
+	/**
+	 * @connector_free_work: Work to clean up @connector_free_list.
+	 */
+	struct work_struct connector_free_work;
+
+	/**
 	 * @num_encoder:
 	 *
 	 * Number of encoders on this device. This is invariant over the