On Mon, Aug 10, 2015 at 11:05:11AM +0000, 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 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 <[email protected]>
>
> Signed-off-by: Aman Deep <[email protected]>
> CC: <[email protected]>
> ---
> drivers/usb/host/ohci-q.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/host/ohci-q.c b/drivers/usb/host/ohci-q.c
> index d029bbe..da878f3 100644
> --- a/drivers/usb/host/ohci-q.c
> +++ b/drivers/usb/host/ohci-q.c
> @@ -1017,6 +1017,8 @@ skip_ed:
> * have modified this list. normally it's just prepending
> * entries (which we'd ignore), but paranoia won't hurt.
> */
> + *last = ed->ed_next;
> + ed->ed_next = NULL;
> modified = 0;
>
> /* unlink urbs as requested, but rescan the list after
> @@ -1075,21 +1077,22 @@ rescan_this:
> goto rescan_this;
>
> /*
> - * If no TDs are queued, take ED off the ed_rm_list.
> + * If no TDs are queued, ED is now idle.
> * Otherwise, if the HC is running, reschedule.
> - * If not, leave it on the list for further dequeues.
> + * If the HC isn't running, add ED back to the
> + * start of the list for later processing.
> */
> if (list_empty(&ed->td_list)) {
> - *last = ed->ed_next;
> - ed->ed_next = NULL;
> ed->state = ED_IDLE;
> list_del(&ed->in_use_list);
> } else if (ohci->rh_state == OHCI_RH_RUNNING) {
> - *last = ed->ed_next;
> - ed->ed_next = NULL;
> ed_schedule(ohci, ed);
> } else {
> - last = &ed->ed_next;
> + ed->ed_next = ohci->ed_rm_list;
> + ohci->ed_rm_list = ed;
> + /* Don't loop on the same ED */
> + if (last == &ohci->ed_rm_list)
> + last = &ed->ed_next;
> }
>
> if (modified)
> --
> 1.7.9.5
This still does not apply properly :(
What tree are you making it against?
thanks,
greg k-h
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