UPSTREAM: usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()

There is a race condition between finish_unlinks->finish_urb() function
and usb_kill_urb() in ohci controller case. The finish_urb calls
spin_unlock(&ohci->lock) before usb_hcd_giveback_urb() function call,
then if during this time, usb_kill_urb is called for another endpoint,
then new ed will be added to ed_rm_list at beginning for unlink, and
ed_rm_list will point to newly added.

When finish_urb() is completed in finish_unlinks() and ed->td_list
becomes empty as in below code (in finish_unlinks() function):

        if (list_empty(&ed->td_list)) {
                *last = ed->ed_next;
                ed->ed_next = NULL;
        } else if (ohci->rh_state == OHCI_RH_RUNNING) {
                *last = ed->ed_next;
                ed->ed_next = NULL;
                ed_schedule(ohci, ed);

The *last = ed->ed_next will make ed_rm_list to point to ed->ed_next
and previously added ed by usb_kill_urb will be left unreferenced by
ed_rm_list. This causes usb_kill_urb() hang forever waiting for
finish_unlink to remove added ed from ed_rm_list.

The main reason for hang in this race condtion is addition and removal
of ed from ed_rm_list in the beginning during usb_kill_urb and later
last* is modified in finish_unlinks().

As suggested by Alan Stern, the solution for proper handling of
ohci->ed_rm_list is to remove ed from the ed_rm_list before finishing
any URBs. Then at the end, we can add ed back to the list if necessary.

This properly handle the updated ohci->ed_rm_list in usb_kill_urb().

Fixes: 977dcfdc6031 ("USB: OHCI: don't lose track of EDs when a controller dies")
Acked-by: Alan Stern <>
CC: <>
Signed-off-by: Aman Deep <>
Signed-off-by: Jeffy Chen <>
Signed-off-by: Greg Kroah-Hartman <>
(cherry picked from commit 46408ea558df13b110e0866b99624384a33bdeba)

TEST=Build and boot

Change-Id: I471f06499fbbc7b98d33a0088dc69dda5b0a546d
Signed-off-by: Jeffy Chen <>
Reviewed-by: Brian Norris <>
Reviewed-by: Matthias Kaehlcke <>
Commit-Queue: Brian Norris <>
1 file changed