On Sat, Jul 11, 2015 at 12:04:26PM +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 <stern@xxxxxxxxxxxxxxxxxxx>
>
> Signed-off-by: Aman Deep <aman.deep@xxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx>
> ---
> 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 f7d561e..496658b 100644
> --- a/drivers/usb/host/ohci-q.c
> +++ b/drivers/usb/host/ohci-q.c
> @@ -1023,6 +1023,8 @@ ed_idle:
> * 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
> @@ -1081,20 +1083,21 @@ 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;
> 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)
> --
This patch doesn't apply to my tree, can you please refresh the patch
agasint 4.2-rc3 and resend it so that I can apply it?
Also, please try to fix your email client to not send base64 patches,
that made it really hard for me to try to figure out what was wrong with
it...
thanks,
greg k-h
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