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 <st...@rowland.harvard.edu>
Signed-off-by: Aman Deep <aman.d...@samsung.com>
CC: <sta...@vger.kernel.org>
---
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
