USB: EHCI: rescan the queue after an unlink

This patch (as1280) fixes an obscure bug in ehci-hcd's dequeuing logic
for async URBs.  If a later URB is unlinked and the completion
routine unlinks an earlier URB, then the earlier URB won't be given
back in a timely manner because the endpoint queue isn't rescanned as
it should be.

Similar bugs occur if an endpoint is reset or a halt is cleared while
a completion routine is running, because the subroutines don't test
for the COMPLETING state.

All these problems are solved by adding a new needs_rescan flag to the
ehci_qh structure.  If the flag is set while scanning through an idle
QH, the scan will be repeated.  If the QH isn't idle then an unlink
cycle will be initiated, and the proper action will be taken when it
becomes idle.

Also, an unnecessary test is removed from qh_link_async(): That
routine is never called if the QH's state isn't IDLE.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 13 insertions, 5 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 6887aac5e73d..d7e85b6231b3 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -863,12 +863,18 @@ static void unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
         if (!HC_IS_RUNNING(ehci_to_hcd(ehci)->state) && ehci->reclaim)
                 end_unlink_async(ehci);
 
-        /* if it's not linked then there's nothing to do */
-        if (qh->qh_state != QH_STATE_LINKED)
-                ;
+        /* If the QH isn't linked then there's nothing we can do
+         * unless we were called during a giveback, in which case
+         * qh_completions() has to deal with it.
+         */
+        if (qh->qh_state != QH_STATE_LINKED) {
+                if (qh->qh_state == QH_STATE_COMPLETING)
+                        qh->needs_rescan = 1;
+                return;
+        }
 
         /* defer till later if busy */
-        else if (ehci->reclaim) {
+        if (ehci->reclaim) {
                 struct ehci_qh          *last;
 
                 for (last = ehci->reclaim;
@@ -1001,6 +1007,7 @@ rescan:
                 qh->qh_state = QH_STATE_IDLE;
         switch (qh->qh_state) {
         case QH_STATE_LINKED:
+        case QH_STATE_COMPLETING:
                 for (tmp = ehci->async->qh_next.qh;
                                 tmp && tmp != qh;
                                 tmp = tmp->qh_next.qh)
@@ -1065,7 +1072,8 @@ ehci_endpoint_reset(struct usb_hcd *hcd, struct usb_host_endpoint *ep)
                 usb_settoggle(qh->dev, epnum, is_out, 0);
                 if (!list_empty(&qh->qtd_list)) {
                         WARN_ONCE(1, "clear_halt for a busy endpoint\n");
-                } else if (qh->qh_state == QH_STATE_LINKED) {
+                } else if (qh->qh_state == QH_STATE_LINKED ||
+                                qh->qh_state == QH_STATE_COMPLETING) {
 
                         /* The toggle value in the QH can't be updated
                          * while the QH is active.  Unlink it now;