drm: safely free connectors from connector_iter

In

commit 613051dac40da1751ab269572766d3348d45a197
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Dec 14 00:08:06 2016 +0100

    drm: locking&new iterators for connector_list

we've went to extreme lengths to make sure connector iterations works
in any context, without introducing any additional locking context.
This worked, except for a small fumble in the implementation:

When we actually race with a concurrent connector unplug event, and
our temporary connector reference turns out to be the final one, then
everything breaks: We call the connector release function from
whatever context we happen to be in, which can be an irq/atomic
context. And connector freeing grabs all kinds of locks and stuff.

Fix this by creating a specially safe put function for connetor_iter,
which (in this rare case) punts the cleanup to a worker.

Reported-by: Ben Widawsky <ben@bwidawsk.net>
Cc: Ben Widawsky <ben@bwidawsk.net>
Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
Cc: Dave Airlie <airlied@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: <stable@vger.kernel.org> # v4.11+
Reviewed-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171204204818.24745-1-daniel.vetter@ffwll.ch

1 files changed, 8 insertions, 0 deletions

diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index df9807a3caae..a4649c56ca2f 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -916,6 +916,14 @@ struct drm_connector {
 	uint8_t num_h_tile, num_v_tile;
 	uint8_t tile_h_loc, tile_v_loc;
 	uint16_t tile_h_size, tile_v_size;
+
+	/**
+	 * @free_work:
+	 *
+	 * Work used only by &drm_connector_iter to be able to clean up a
+	 * connector from any context.
+	 */
+	struct work_struct free_work;
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)