From 6abe8fe36b29ff51d1a42c2f338972883f4751a5 Mon Sep 17 00:00:00 2001 From: Sudeep Holla Date: Tue, 14 Jul 2026 13:56:34 +0100 Subject: [PATCH] firmware: arm_scmi: Fix SCMI device destroy lifetimes scmi_child_dev_find() drops the reference returned by device_find_child() before returning the scmi_device pointer. A concurrent unregister can then release the device while the destroy path is still using the returned pointer. Make the lookup helper return the device_find_child() reference and keep it until scmi_device_destroy() has finished unregistering the child. Also split device_unregister() in __scmi_device_destroy() so the SCMI bus ID is not made reusable until after device_del() has removed the old scmi_dev.N name from sysfs. This avoids a new SCMI device reusing the same ID while the old device is still registered. The final device release callback is also a possible cleanup path when SCMI children are deleted by driver core recursion rather than __scmi_device_destroy(). Release the SCMI bus ID from a common helper used by destroy, register-failure and final-release paths, and clear scmi_dev->id after freeing it so the final release cannot free the same ID again. Fixes: 9ca67840c0dd ("firmware: arm_scmi: Balance device refcount when destroying devices") Reported-by: Sashiko Link: https://patch.msgid.link/20260714-scmi_core_fixes-v6-15-3afe499d46e3@kernel.org Signed-off-by: Sudeep Holla --- drivers/firmware/arm_scmi/bus.c | 39 +++++++++++++++++++-------------- 1 file changed, 23 insertions(+), 16 deletions(-) diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c index a14df82a9310..e1f66c08c81d 100644 --- a/drivers/firmware/arm_scmi/bus.c +++ b/drivers/firmware/arm_scmi/bus.c @@ -237,8 +237,9 @@ static int scmi_match_by_id_table(struct device *dev, const void *data) return scmi_dev_match_by_id_table(scmi_dev, id_table); } -static struct scmi_device *scmi_child_dev_find(struct device *parent, - int prot_id, const char *name) +/* Returns a device_find_child() reference which must be dropped by caller. */ +static struct scmi_device * +scmi_child_dev_find_get(struct device *parent, int prot_id, const char *name) { struct scmi_device_id id_table[2] = { 0 }; struct device *dev; @@ -250,9 +251,6 @@ static struct scmi_device *scmi_child_dev_find(struct device *parent, if (!dev) return NULL; - /* Drop the refcnt bumped implicitly by device_find_child */ - put_device(dev); - return to_scmi_dev(dev); } @@ -390,17 +388,22 @@ void scmi_driver_unregister(struct scmi_driver *driver) } EXPORT_SYMBOL_GPL(scmi_driver_unregister); -static void scmi_device_release_syspower(struct scmi_device *scmi_dev) +static void scmi_device_release_resources(struct scmi_device *scmi_dev) { if (scmi_dev->protocol_id == SCMI_PROTOCOL_SYSTEM) cmpxchg(&scmi_syspower_registered, scmi_dev, NULL); + + if (scmi_dev->id) { + ida_free(&scmi_bus_id, scmi_dev->id); + scmi_dev->id = 0; + } } static void scmi_device_release(struct device *dev) { struct scmi_device *scmi_dev = to_scmi_dev(dev); - scmi_device_release_syspower(scmi_dev); + scmi_device_release_resources(scmi_dev); of_node_put(dev->of_node); kfree_const(scmi_dev->name); kfree(scmi_dev); @@ -413,9 +416,9 @@ static void __scmi_device_destroy(struct scmi_device *scmi_dev) dev_name(&scmi_dev->dev), scmi_dev->protocol_id, scmi_dev->name); - scmi_device_release_syspower(scmi_dev); - ida_free(&scmi_bus_id, scmi_dev->id); - device_unregister(&scmi_dev->dev); + device_del(&scmi_dev->dev); + scmi_device_release_resources(scmi_dev); + put_device(&scmi_dev->dev); } static struct scmi_device * @@ -433,9 +436,11 @@ __scmi_device_create(struct device_node *np, struct device *parent, * each DT defined protocol at probe time, and the concurrent * registration of SCMI drivers. */ - scmi_dev = scmi_child_dev_find(parent, protocol, name); - if (scmi_dev) + scmi_dev = scmi_child_dev_find_get(parent, protocol, name); + if (scmi_dev) { + put_device(&scmi_dev->dev); return scmi_dev; + } scmi_dev = kzalloc_obj(*scmi_dev); if (!scmi_dev) @@ -479,13 +484,13 @@ __scmi_device_create(struct device_node *np, struct device *parent, return scmi_dev; put_dev: + scmi_device_release_resources(scmi_dev); put_device(&scmi_dev->dev); - ida_free(&scmi_bus_id, id); return NULL; free_name: kfree_const(scmi_dev->name); free_dev: - scmi_device_release_syspower(scmi_dev); + scmi_device_release_resources(scmi_dev); kfree(scmi_dev); return NULL; } @@ -567,9 +572,11 @@ void scmi_device_destroy(struct device *parent, int protocol, const char *name) { struct scmi_device *scmi_dev; - scmi_dev = scmi_child_dev_find(parent, protocol, name); - if (scmi_dev) + scmi_dev = scmi_child_dev_find_get(parent, protocol, name); + if (scmi_dev) { __scmi_device_destroy(scmi_dev); + put_device(&scmi_dev->dev); + } } EXPORT_SYMBOL_GPL(scmi_device_destroy);