The SCSI core does not like to have devices or hosts unregistered while error recovery is in progress. Trying to do so can lead to self-deadlock: Part of the removal code tries to obtain a lock already held by the error handler. This can cause problems for the usb-storage and uas drivers, because their error handler routines perform a USB reset, and if the reset fails then the USB core automatically goes on to unbind all drivers from the device's interfaces -- all while still in the context of the SCSI error handler. As it turns out, practically all the scenarios leading to a USB reset failure end up causing a device disconnect (the main error pathway in usb_reset_and_verify_device(), at the end of the routine, calls hub_port_logical_disconnect() before returning). As a result, the hub_wq thread will soon become aware of the problem and will unbind all the device's drivers in its own context, not in the error-handler's context. This means that usb_reset_device() does not need to call usb_unbind_and_rebind_marked_interfaces() in cases where usb_reset_and_verify_device() has returned an error, because hub_wq will take care of everything anyway. This particular problem was observed in somewhat artificial circumstances, by using usbfs to tell a hub to power-down a port connected to a USB-3 mass storage device using the UAS protocol. With the port turned off, the currently executing command timed out and the error handler started running. The USB reset naturally failed, because the hub port was off, and the error handler deadlocked as described above. Not carrying out the call to usb_unbind_and_rebind_marked_interfaces() fixes this issue. Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Reported-by: Kento Kobayashi <Kento.A.Kobayashi@xxxxxxxx> Tested-by: Kento Kobayashi <Kento.A.Kobayashi@xxxxxxxx> CC: Bart Van Assche <bvanassche@xxxxxxx> CC: Martin K. Petersen <martin.petersen@xxxxxxxxxx> CC: Jacky Cao <Jacky.Cao@xxxxxxxx> --- [as1885] drivers/usb/core/hub.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) Index: usb-4.x/drivers/usb/core/hub.c =================================================================== --- usb-4.x.orig/drivers/usb/core/hub.c +++ usb-4.x/drivers/usb/core/hub.c @@ -5902,7 +5902,10 @@ int usb_reset_device(struct usb_device * cintf->needs_binding = 1; } } - usb_unbind_and_rebind_marked_interfaces(udev); + + /* If the reset failed, hub_wq will unbind drivers later */ + if (ret == 0) + usb_unbind_and_rebind_marked_interfaces(udev); } usb_autosuspend_device(udev);
