Quoting Daniel Vetter (2017-12-13 10:45:53)
> 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.
>
> Fixes: a703c55004e1 ("drm: safely free connectors from connector_iter")
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Ben Widawsky <ben@xxxxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.11+: 613051dac40d ("drm: locking&new iterators for connector_list"
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.11+
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Javier Martinez Canillas <javier@xxxxxxxxxxxx>
> Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> Cc: Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxxxxxxxx>
> Cc: Matt Hart <matthew.hart@xxxxxxxxxx>
> Cc: Thierry Escande <thierry.escande@xxxxxxxxxxxxxxx>
> Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> Cc: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
> drivers/gpu/drm/drm_connector.c | 46 ++++++++++++++++++++++++++-----------
> drivers/gpu/drm/drm_crtc_internal.h | 1 +
> drivers/gpu/drm/drm_mode_config.c | 5 +++-
> include/drm/drm_connector.h | 4 ++--
> include/drm/drm_mode_config.h | 17 +++++++++++++-
> 5 files changed, 55 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 0b7e0974e6da..2f43dc217936 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;
> + 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;
> + LIST_HEAD(list_head);
>
> - drm_mode_object_unregister(dev, &connector->base);
> - connector->funcs->destroy(connector);
> + spin_lock_irqsave(&config->connector_list_lock, flags);
> + list_splice(&config->connector_free_list, &list_head);
> + spin_unlock_irqrestore(&config->connector_list_lock, flags);
> +
> + list_for_each_entry(connector, &list_head, free_head) {
> + 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 +557,15 @@ 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)
> {
> + struct drm_mode_config *config = &conn->dev->mode_config;
> +
> + lockdep_assert_held(&config->connector_list_lock);
> + list_add(&conn->free_head, &config->connector_free_list);
Adding to the free_list before refcount==0?
May I suggest,
if (!refcount_dec_and_test())
return;
if (llist_add(&conn->free_link, &config->connector_free_list))
schedule_work(&config->connector_free_work);
llist being much more friendly for freelists:
void drm_connector_free_work_fn(struct work_struct *work)
{
struct drm_device *dev =
container_of(work, struct drm_device, mode_config.connector_free_work);
struct drm_mode_config *config = &dev->mode_config;
struct drm_connector *connector, *n;
struct llist_node *freed;
freed = llist_del_all(config->connector_free_list);
llist_for_each_entry_safe(connector, n, freed, free_link) {
drm_mode_object_unregister(dev, &connector->base);
connector->funcs->destroy(connector);
}
}
-Chris