USB: EHCI: fix for leaking isochronous data

This patch (as1653) fixes a bug in ehci-hcd.  Unlike iTD entries, an
siTD entry in the periodic schedule may not complete until the frame
after the one it belongs to.  Consequently, when scanning the periodic
schedule it is necessary to start with the frame _preceding_ the one
where the previous scan ended.

Not doing this properly can result in memory leaks and failures to
complete isochronous URBs.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andy Leiserson <andy@leiserson.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-sched.c

@@ -2212,11 +2212,11 @@ static void scan_isoc(struct ehci_hcd *ehci)
 	}
 	ehci->now_frame = now_frame;
 
+	frame = ehci->last_iso_frame;
 	for (;;) {
 		union ehci_shadow	q, *q_p;
 		__hc32			type, *hw_p;
 
-		frame = ehci->last_iso_frame;
 restart:
 		/* scan each element in frame's queue for completions */
 		q_p = &ehci->pshadow [frame];
@@ -2321,6 +2321,9 @@ restart:
 		/* Stop when we have reached the current frame */
 		if (frame == now_frame)
 			break;
-		ehci->last_iso_frame = (frame + 1) & fmask;
+
+		/* The last frame may still have active siTDs */
+		ehci->last_iso_frame = frame;
+		frame = (frame + 1) & fmask;
 	}
 }