In
commit 613051dac40da1751ab269572766d3348d45a197
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
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@xxxxxxxxxxxx>
Cc: Ben Widawsky <ben@xxxxxxxxxxxx>
Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
Cc: Dave Airlie <airlied@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.11+
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
drivers/gpu/drm/drm_connector.c | 28 ++++++++++++++++++++++++++--
drivers/gpu/drm/drm_mode_config.c | 2 ++
include/drm/drm_connector.h | 8 ++++++++
3 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 25f4b2e9a44f..482014137953 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -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);
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 7623607c0f1e..346c19c6ce01 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -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)
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 66d6c99d15e5..c5c753a1be85 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -926,6 +926,14 @@ 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)
--
2.15.0