On Thu, 17 Jul 2003, Johannes Erdfelt wrote: > On Thu, Jul 17, 2003, Alan Stern <[EMAIL PROTECTED]> wrote: > > A bug has turned up in the UHCI driver. Briefly, when an URB completes, > > uhci_transfer_result() doesn't store the status in urb->status but only in > > urbp->status. urb->status is set just before calling hcd_giveback_urb(). > > > > However, the hcd glue layer uses urb->status == -EINPROGRESS as a test for > > whether or not to allow the URB to be unlinked. As a result, it's > > possible to unlink an URB after it has completed and is already on the > > urb_complete_list. This causes severe problems. > > This check is kinda racy in the first place, but I can see the problem > with the current code.
The race isn't so bad, since all the accesses to urb->status are protected by urb->lock. > > My suggestion is to set urb->status along with urbp->status in > > uhci_transfer_result(). In fact, looking through the code it appears that > > urbp->status is completely unnecessary, since it should pretty much always > > be equal to urb->status. Is there any reason for keeping urbp->status? > > I actually added urbp->status to fix a bug in 2.4. > > I don't think it applies to 2.4 or 2.5/2.6 anymore. I think we can > probably clean that up. I'll work on a patch over the weekend. > > P.S.: In addition, when URBs are dequeued, they should be added to the > > _tail_ of remove_list. That way the completion handlers will be called in > > the order the URBs were unlinked. > > I assume you mean urb_remove_list? Looking at the code now, I have no > idea why I named it uhci_remove_pending_qhs(), since it has nothing to > do with QHs, only URBs. I wondered about that myself. > The idea was to delay completing the URBs because the QH/TDs might still > be in use by the HC until the next frame. Just as with a normally completed URB, since its QH could still be accessed by the HC until the next frame. Alan Stern ------------------------------------------------------- This SF.net email is sponsored by: VM Ware With VMware you can run multiple operating systems on a single machine. WITHOUT REBOOTING! Mix Linux / Windows / Novell virtual machines at the same time. Free trial click here: http://www.vmware.com/wl/offer/345/0 _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
