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@xxxxxxxxxxxxxxx
Signed-off-by: Elson Roy Serrao <quic_eserrao@xxxxxxxxxxx>
---
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@xxxxxxxxxxx/
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;
put_device(&sw->dev);
return ERR_PTR(ret);
}
@@ -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
