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

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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: 977dcfdc60 ("USB: OHCI: don't lose track of EDs when a controller dies")
Acked-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>
Signed-off-by: Aman Deep <aman.deep@samsung.com>
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
AMAN DEEP 2018-02-08 11:55:01 +08:00 committed by Greg Kroah-Hartman
parent 91b119359c
commit 46408ea558
1 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
drivers/usb/host/ohci-q.c
View File

@ -1019,6 +1019,8 @@ 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
@ -1077,21 +1079,22 @@ 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)