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Commit a703c550 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

drm: safely free connectors from connector_iter 



In

commit 613051da
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: default avatarBen Widawsky <ben@bwidawsk.net>
Cc: Ben Widawsky <ben@bwidawsk.net>
Fixes: 613051da ("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: default avatarDave Airlie <airlied@gmail.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171204204818.24745-1-daniel.vetter@ffwll.ch
parent ae64f9bd

drivers/gpu/drm/drm_connector.c

+26 −2
Original line number Diff line number Diff line
@@ -152,6 +152,16 @@ static void drm_connector_free(struct kref *kref) 
	connector->funcs->destroy(connector);

}



static void drm_connector_free_work_fn(struct work_struct *work)

{

	struct drm_connector *connector =

		container_of(work, struct drm_connector, free_work);

	struct drm_device *dev = connector->dev;



	drm_mode_object_unregister(dev, &connector->base);

	connector->funcs->destroy(connector);

}



/**

 * drm_connector_init - Init a preallocated connector

 * @dev: DRM device
@@ -181,6 +191,8 @@ int drm_connector_init(struct drm_device *dev, 
	if (ret)

		return ret;



	INIT_WORK(&connector->free_work, drm_connector_free_work_fn);



	connector->base.properties = &connector->properties;

	connector->dev = dev;

	connector->funcs = funcs;
@@ -529,6 +541,18 @@ void drm_connector_list_iter_begin(struct drm_device *dev, 
}

EXPORT_SYMBOL(drm_connector_list_iter_begin);



/*

 * Extra-safe connector put function that works in any context. Should only be

 * used from the connector_iter functions, where we never really expect to

 * actually release the connector when dropping our final reference.

 */

static void

drm_connector_put_safe(struct drm_connector *conn)

{

	if (refcount_dec_and_test(&conn->base.refcount.refcount))

		schedule_work(&conn->free_work);

}



/**

 * drm_connector_list_iter_next - return next connector

 * @iter: connectr_list iterator
@@ -561,7 +585,7 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter) 
	spin_unlock_irqrestore(&config->connector_list_lock, flags);



	if (old_conn)

		drm_connector_put(old_conn);

		drm_connector_put_safe(old_conn);



	return iter->conn;

}
@@ -580,7 +604,7 @@ void drm_connector_list_iter_end(struct drm_connector_list_iter *iter) 
{

	iter->dev = NULL;

	if (iter->conn)

		drm_connector_put(iter->conn);

		drm_connector_put_safe(iter->conn);

	lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);

}

EXPORT_SYMBOL(drm_connector_list_iter_end);

drivers/gpu/drm/drm_mode_config.c

+2 −0
Original line number Diff line number Diff line
@@ -431,6 +431,8 @@ void drm_mode_config_cleanup(struct drm_device *dev) 
		drm_connector_put(connector);

	}

	drm_connector_list_iter_end(&conn_iter);

	/* connector_iter drops references in a work item. */

	flush_scheduled_work();

	if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {

		drm_connector_list_iter_begin(dev, &conn_iter);

		drm_for_each_connector_iter(connector, &conn_iter)

include/drm/drm_connector.h

+8 −0
Original line number Diff line number Diff line
@@ -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)