On Thu, 9 Jul 2015, AMAN DEEP wrote:
> 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
> ed.
>
> 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);
> }
> *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 handles the updated ohci->ed_rm_list in
> usb_kill_urb().
>
> Signed-off-by: Aman Deep <aman.deep@xxxxxxxxxxx>
This patch should have a "CC: <stable@xxxxxxxxxxxxxxx>" tag, since
older kernels contain the same bug. And there should also be a tag
saying
Fixes: 977dcfdc6031 ("USB: OHCI: don't lose track of EDs when a controller dies")
since that is the commit which introduced this bug. When you add those
two, you may also add:
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Alan Stern
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