[PATCH 7/7] soundwire: bus: Fix premature removal of sdw_slave objects

Richard Fitzgerald
2022-09-07T10:15:36Z

When the bus manager is removed sdw_bus_master_delete() should not
be deleting the struct sdw_slave objects until the bus manager has
been stopped. The first step of removing child drivers should only
be calling device_unregister() on the child. The counterpart to
sdw_drv_probe() is sdw_drv_remove(), not sdw_delete_slave().

The sdw_slave objects are created by the bus manager probe() from
ACPI/DT information. They are not created when a child driver probes
so should not be deleted by a child driver remove.

Change-Id: I25cc145df12fdc7c126f8f594a5f76eedce25488
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
---
drivers/soundwire/bus.c | 30 ++++++++++++++++++++++++++----
drivers/soundwire/slave.c | 21 +++++++++++++++++----
2 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 1327a312be86..5533eb589286 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -146,9 +146,8 @@ int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent,
}
EXPORT_SYMBOL(sdw_bus_master_add);

-static int sdw_delete_slave(struct device *dev, void *data)
+static int sdw_delete_slave(struct sdw_slave *slave)
{
- struct sdw_slave *slave = dev_to_sdw_dev(dev);
struct sdw_bus *bus = slave->bus;

sdw_slave_debugfs_exit(slave);
@@ -163,7 +162,24 @@ static int sdw_delete_slave(struct device *dev, void *data)
list_del_init(&slave->node);
mutex_unlock(&bus->bus_lock);

+ mutex_destroy(&slave->sdw_dev_lock);
+ kfree(slave);
+
+ return 0;
+}
+
+static int sdw_remove_child(struct device *dev, void *data)
+{
+ /*
+ * Do not remove the struct sdw_slave yet. This is created by
+ * the bus manager probe() from ACPI information and used by the
+ * bus manager to hold status of each peripheral. Its lifetime
+ * is that of the bus manager.
+ */
+
+ /* This will call sdw_drv_remove() */
device_unregister(dev);
+
return 0;
}

@@ -171,16 +187,22 @@ static int sdw_delete_slave(struct device *dev, void *data)
* sdw_bus_master_delete() - delete the bus master instance
* @bus: bus to be deleted
*
- * Remove the instance, delete the child devices.
+ * Remove the child devices, remove the master instance.
*/
void sdw_bus_master_delete(struct sdw_bus *bus)
{
- device_for_each_child(bus->dev, NULL, sdw_delete_slave);
+ struct sdw_slave *slave, *tmp;
+
+ device_for_each_child(bus->dev, NULL, sdw_remove_child);

/* Children have been removed so it is now safe for the bus to stop */
if (bus->ops->remove)
bus->ops->remove(bus);

+ /* Now the bus is stopped it is safe to free things */
+ list_for_each_entry_safe(slave, tmp, &bus->slaves, node)
+ sdw_delete_slave(slave);
+
sdw_master_device_del(bus);

sdw_bus_debugfs_exit(bus);
diff --git a/drivers/soundwire/slave.c b/drivers/soundwire/slave.c
index c1c1a2ac293a..b6161d002b97 100644
--- a/drivers/soundwire/slave.c
+++ b/drivers/soundwire/slave.c
@@ -10,10 +10,23 @@

static void sdw_slave_release(struct device *dev)
{
- struct sdw_slave *slave = dev_to_sdw_dev(dev);
-
- mutex_destroy(&slave->sdw_dev_lock);
- kfree(slave);
+ /*
+ * The release() callback should not be empty
+ * (see Documentation/core-api/kobject.rst) but the ownership
+ * of struct sdw_slave is muddled. It is used for two separate
+ * purposes:
+ * 1) by the bus driver to track its own state information for
+ * physical devices on the bus and found in ACPI/DT, whether
+ * or not there is a child driver for it;
+ * 2) to hold the child driver object.
+ *
+ * The struct sdw_slave cannot be freed when the child driver
+ * is released because it is holding info used by the bus
+ * driver. It is freed when the bus driver is removed.
+ *
+ * Until the ownership issue is untangled this cannot free
+ * the struct sdw_slave object containing the child dev.
+ */
}

struct device_type sdw_slave_type = {
--
2.30.2