[PATCH v2 1/2] driver: core: add dedicated workqueue for devlink removal

Nuno Sa via B4 Relay
2024-02-05T12:09:34Z

From: Nuno Sa <nuno.sa@analog.com>

Let's use a dedicated queue for devlinks since releasing a link happens
asynchronously but some code paths, like DT overlays, have some
expectations regarding the of_node when being removed (the refcount must
be 1). Given how devlinks are released that cannot be assured. Hence, add a
dedicated queue so that it's easy to sync against devlinks removal.

While at it, make sure to explicitly include <linux/workqueue.h>.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
drivers/base/core.c | 32 ++++++++++++++++++++++++++++----
include/linux/fwnode.h | 1 +
2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 14d46af40f9a..4bb9c10489ed 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -31,6 +31,7 @@
#include <linux/swiotlb.h>
#include <linux/sysfs.h>
#include <linux/dma-map-ops.h> /* for dma_default_coherent */
+#include <linux/workqueue.h>

#include "base.h"
#include "physical_location.h"
@@ -44,6 +45,7 @@ static bool fw_devlink_is_permissive(void);
static void __fw_devlink_link_to_consumers(struct device *dev);
static bool fw_devlink_drv_reg_done;
static bool fw_devlink_best_effort;
+static struct workqueue_struct *devlink_release_queue __ro_after_init;

/**
* __fwnode_link_add - Create a link between two fwnode_handles.
@@ -235,6 +237,12 @@ static void __fw_devlink_pickup_dangling_consumers(struct fwnode_handle *fwnode,
__fw_devlink_pickup_dangling_consumers(child, new_sup);
}

+void fwnode_links_flush_queue(void)
+{
+ if (devlink_release_queue)
+ flush_workqueue(devlink_release_queue);
+}
+
static DEFINE_MUTEX(device_links_lock);
DEFINE_STATIC_SRCU(device_links_srcu);

@@ -531,9 +539,13 @@ static void devlink_dev_release(struct device *dev)
* It may take a while to complete this work because of the SRCU
* synchronization in device_link_release_fn() and if the consumer or
* supplier devices get deleted when it runs, so put it into the "long"
- * workqueue.
+ * devlink workqueue (in case we could allocate one).
+ *
*/
- queue_work(system_long_wq, &link->rm_work);
+ if (devlink_release_queue)
+ queue_work(devlink_release_queue, &link->rm_work);
+ else
+ device_link_release_fn(&link->rm_work);
}

static struct class devlink_class = {
@@ -636,10 +648,22 @@ static int __init devlink_class_init(void)
return ret;

ret = class_interface_register(&devlink_class_intf);
- if (ret)
+ if (ret) {
class_unregister(&devlink_class);
+ return ret;
+ }

- return ret;
+ /*
+ * Using a dedicated queue for devlinks since releasing a link happens
+ * asynchronously but some code paths, like DT overlays, have some
+ * expectations regarding the of_node when being removed (the refcount
+ * must be 1). Given how devlinks are released that cannot be assured.
+ * Hence, add a dedicated queue so that it's easy to sync against
+ * devlinks removal.
+ */
+ devlink_release_queue = alloc_workqueue("devlink_release", 0, 0);
+
+ return 0;
}
postcore_initcall(devlink_class_init);

diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 2a72f55d26eb..017b170e9903 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -213,5 +213,6 @@ extern bool fw_devlink_is_strict(void);
int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup);
void fwnode_links_purge(struct fwnode_handle *fwnode);
void fw_devlink_purge_absent_suppliers(struct fwnode_handle *fwnode);
+void fwnode_links_flush_queue(void);

#endif

--
2.43.0