From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailout1.w1.samsung.com ([210.118.77.11]:44781 "EHLO mailout1.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752175AbdLMNBT (ORCPT ); Wed, 13 Dec 2017 08:01:19 -0500 Subject: Re: [PATCH] drm: rework delayed connector cleanup in connector_iter To: Daniel Vetter , Intel Graphics Development Cc: Ben Widawsky , Tomeu Vizoso , David Airlie , Mark Brown , Shuah Khan , DRI Development , Thierry Escande , Guillaume Tucker , stable@vger.kernel.org, Enric Balletbo i Serra , Daniel Vetter , Javier Martinez Canillas , Kevin Hilman , Matt Hart From: Marek Szyprowski Message-id: Date: Wed, 13 Dec 2017 14:01:14 +0100 MIME-version: 1.0 In-reply-to: <20171213124936.17914-1-daniel.vetter@ffwll.ch> Content-type: text/plain; charset="utf-8"; format="flowed" Content-transfer-encoding: 7bit Content-language: en-US References: <20171213104553.30821-1-daniel.vetter@ffwll.ch> <20171213124936.17914-1-daniel.vetter@ffwll.ch> Sender: stable-owner@vger.kernel.org List-ID: 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 > Cc: Dave Airlie > Cc: Chris Wilson > Cc: Sean Paul > Cc: # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list" > Cc: # v4.11+ > Cc: Daniel Vetter > Cc: Jani Nikula > Cc: Gustavo Padovan > Cc: David Airlie > Cc: Javier Martinez Canillas > Cc: Shuah Khan > Cc: Guillaume Tucker > Cc: Mark Brown > Cc: Kevin Hilman > Cc: Matt Hart > Cc: Thierry Escande > Cc: Tomeu Vizoso > Cc: Enric Balletbo i Serra > Signed-off-by: Daniel Vetter This one works fine and fixes deadlock in my test environment. Tested-by: Marek Szyprowski > --- > 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 > +#include > #include > #include > #include > @@ -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 > #include > #include > +#include > > #include > > @@ -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