[PATCH] drm: rework delayed connector cleanup in connector_iter
Marek Szyprowski
m.szyprowski at samsung.com
Wed Dec 13 13:01:14 UTC 2017
Hi Daniel,
On 2017-12-13 13:49, Daniel Vetter wrote:
> 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).
>
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben at bwidawsk.net>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: <stable at vger.kernel.org> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable at vger.kernel.org> # v4.11+
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Gustavo Padovan <gustavo at padovan.org>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Javier Martinez Canillas <javier at dowhile0.org>
> Cc: Shuah Khan <shuahkh at osg.samsung.com>
> Cc: Guillaume Tucker <guillaume.tucker at collabora.com>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Kevin Hilman <khilman at baylibre.com>
> Cc: Matt Hart <matthew.hart at linaro.org>
> Cc: Thierry Escande <thierry.escande at collabora.co.uk>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Enric Balletbo i Serra <enric.balletbo at collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
This one works fine and fixes deadlock in my test environment.
Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
> ---
> drivers/gpu/drm/drm_connector.c | 50 ++++++++++++++++++++++++++-----------
> drivers/gpu/drm/drm_crtc_internal.h | 1 +
> drivers/gpu/drm/drm_mode_config.c | 4 ++-
> include/drm/drm_connector.h | 10 +++++---
> include/drm/drm_mode_config.h | 18 ++++++++++++-
> 5 files changed, 62 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..3f53f127e1f2 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -153,14 +153,23 @@ static void drm_connector_free(struct kref *kref)
> connector->funcs->destroy(connector);
> }
>
> -static void drm_connector_free_work_fn(struct work_struct *work)
> +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;
> + struct drm_connector *connector, *n;
> + struct drm_device *dev =
> + container_of(work, struct drm_device, mode_config.connector_free_work);
> + struct drm_mode_config *config = &dev->mode_config;
> + unsigned long flags;
> + struct llist_node *freed;
>
> - drm_mode_object_unregister(dev, &connector->base);
> - connector->funcs->destroy(connector);
> + spin_lock_irqsave(&config->connector_list_lock, flags);
> + freed = llist_del_all(&config->connector_free_list);
> + spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +
> + llist_for_each_entry_safe(connector, n, freed, free_node) {
> + drm_mode_object_unregister(dev, &connector->base);
> + connector->funcs->destroy(connector);
> + }
> }
>
> /**
> @@ -192,8 +201,6 @@ 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;
> @@ -550,10 +557,17 @@ EXPORT_SYMBOL(drm_connector_list_iter_begin);
> * actually release the connector when dropping our final reference.
> */
> static void
> -drm_connector_put_safe(struct drm_connector *conn)
> +__drm_connector_put_safe(struct drm_connector *conn)
> {
> - if (refcount_dec_and_test(&conn->base.refcount.refcount))
> - schedule_work(&conn->free_work);
> + struct drm_mode_config *config = &conn->dev->mode_config;
> +
> + lockdep_assert_held(&config->connector_list_lock);
> +
> + if (!refcount_dec_and_test(&conn->base.refcount.refcount))
> + return;
> +
> + llist_add(&conn->free_node, &config->connector_free_list);
> + schedule_work(&config->connector_free_work);
> }
>
> /**
> @@ -585,10 +599,10 @@ drm_connector_list_iter_next(struct drm_connector_list_iter *iter)
>
> /* loop until it's not a zombie connector */
> } while (!kref_get_unless_zero(&iter->conn->base.refcount));
> - spin_unlock_irqrestore(&config->connector_list_lock, flags);
>
> if (old_conn)
> - drm_connector_put_safe(old_conn);
> + __drm_connector_put_safe(old_conn);
> + spin_unlock_irqrestore(&config->connector_list_lock, flags);
>
> return iter->conn;
> }
> @@ -605,9 +619,15 @@ EXPORT_SYMBOL(drm_connector_list_iter_next);
> */
> void drm_connector_list_iter_end(struct drm_connector_list_iter *iter)
> {
> + struct drm_mode_config *config = &iter->dev->mode_config;
> + unsigned long flags;
> +
> iter->dev = NULL;
> - if (iter->conn)
> - drm_connector_put_safe(iter->conn);
> + if (iter->conn) {
> + spin_lock_irqsave(&config->connector_list_lock, flags);
> + __drm_connector_put_safe(iter->conn);
> + spin_unlock_irqrestore(&config->connector_list_lock, flags);
> + }
> lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
> }
> EXPORT_SYMBOL(drm_connector_list_iter_end);
> diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
> index 9ebb8841778c..af00f42ba269 100644
> --- a/drivers/gpu/drm/drm_crtc_internal.h
> +++ b/drivers/gpu/drm/drm_crtc_internal.h
> @@ -142,6 +142,7 @@ int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
> uint64_t value);
> int drm_connector_create_standard_properties(struct drm_device *dev);
> const char *drm_get_connector_force_name(enum drm_connector_force force);
> +void drm_connector_free_work_fn(struct work_struct *work);
>
> /* IOCTL */
> int drm_mode_connector_property_set_ioctl(struct drm_device *dev,
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 6ffe952142e6..7681269abe41 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -382,6 +382,8 @@ void drm_mode_config_init(struct drm_device *dev)
> ida_init(&dev->mode_config.connector_ida);
> spin_lock_init(&dev->mode_config.connector_list_lock);
>
> + INIT_WORK(&dev->mode_config.connector_free_work, drm_connector_free_work_fn);
> +
> drm_mode_create_standard_properties(dev);
>
> /* Just to be sure */
> @@ -432,7 +434,7 @@ void drm_mode_config_cleanup(struct drm_device *dev)
> }
> drm_connector_list_iter_end(&conn_iter);
> /* connector_iter drops references in a work item. */
> - flush_scheduled_work();
> + flush_work(&dev->mode_config.connector_free_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)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index ee3155391243..ed38df4ac204 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>
> @@ -966,12 +967,13 @@ 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 e5f3b43014e1..2cb6f02df64a 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>
>
> @@ -402,7 +403,7 @@ struct drm_mode_config {
>
> /**
> * @connector_list_lock: Protects @num_connector and
> - * @connector_list.
> + * @connector_list and @connector_free_list.
> */
> spinlock_t connector_list_lock;
> /**
> @@ -422,6 +423,21 @@ struct drm_mode_config {
> * &struct drm_connector_list_iter to walk this list.
> */
> 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:
> *
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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