On Thu, Feb 06, 2025 at 11:39:50AM -0800, Elson Roy Serrao wrote:
The role switch registration and set_role() can happen in parallel as they are invoked independent of each other. There is a possibility that a driver might spend significant amount of time in usb_role_switch_register() API due to the presence of time intensive operations like component_add() which operate under common mutex. This leads to a time window after allocating the switch and before setting the registered flag where the set role notifications are dropped. Below timeline summarizes this behavior
Thread1 | Thread2 usb_role_switch_register() | | | ---> allocate switch | | | ---> component_add() | usb_role_switch_set_role() | | | | | --> Drop role notifications | | since sw->registered | | flag is not set. | | --->Set registered flag.|
To avoid this, set the registered flag early on in the switch register API.
Fixes: b787a3e78175 ("usb: roles: don't get/set_role() when usb_role_switch is unregistered") cc: stable@vger.kernel.org Signed-off-by: Elson Roy Serrao quic_eserrao@quicinc.com
Reviewed-by: Heikki Krogerus heikki.krogerus@linux.intel.com
Changes in v2:
- Set the switch registered flag from the get-go as suggested by Heikki.
- Modified subject line and commit next as per the new logic.
- Link to v1: https://lore.kernel.org/all/20250127230715.6142-1-quic_eserrao@quicinc.com/
drivers/usb/roles/class.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c index c58a12c147f4..30482d4cf826 100644 --- a/drivers/usb/roles/class.c +++ b/drivers/usb/roles/class.c @@ -387,8 +387,11 @@ usb_role_switch_register(struct device *parent, dev_set_name(&sw->dev, "%s-role-switch", desc->name ? desc->name : dev_name(parent));
- sw->registered = true;
- ret = device_register(&sw->dev); if (ret) {
sw->registered = false;@@ -399,8 +402,6 @@ usb_role_switch_register(struct device *parent, dev_warn(&sw->dev, "failed to add component\n"); }
- sw->registered = true;
- /* TODO: Symlinks for the host port and the device controller. */
return sw; -- 2.17.1