On Fri, 13 Sep 2013, Bjorn Helgaas wrote: > usb_bus_list_lock protects the usb_bus_list, and we don't touch that list > in usb_disconnect(), so there's no reason to hold the lock here. The code says: /* used when updating list of hcds */ DEFINE_MUTEX(usb_bus_list_lock); /* exported only for usbfs */ EXPORT_SYMBOL_GPL (usb_bus_list_lock); Unforunately, the first comment is incomplete. usb_bus_list_lock protects both the list of buses and also the set of root hubs. That's why it isn't needed in hub_quiesce() and hub_port_connect_change(); those routines remove only non-root devices. Removing the usages in usb_add_hcd() and usb_remove_hcd() isn't safe. You can see where this usage is important in devices.c:usb_device_read(). Ironically, the second comment above is wrong as well. Although usbfs does use the lock, usbfs is part of the same module as hcd.c. Therefore there's no reason to EXPORT usb_bus_list_lock. Alan Stern P.S.: What led you to submit these changes? -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
