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SubjectRe: 2.6.36-rc7: NULL pointer dereference in ehci_clear_tt_buffer_complete
On Sat, 16 Oct 2010, Stefan Richter wrote:

> Alan Stern wrote:
> > On Thu, 14 Oct 2010, Stefan Richter wrote:
> >
> >> Alan Stern wrote:
> >>> Stefan, is it possible for you to tell whether this really does work?
> >> That will be hard. So far I was unable to reproduce the oops; still running
> >> unmodified 2.6.36-rc7.
> >
> > Was this on an SMP machine?
>
> Yes.
>
> > If yes, the untested patch below may help
> > trigger the oops. To use it, insert (but don't mount) a memory card
> > into the card reader, and use dd to copy a large amount of data from
> > the card to /dev/null. While that's running, unplug either the monitor
> > or the card reader. You may want to do this at a VT console so you can
> > see directly when the delay occurs.
> >
> > Alan Stern
> >
> >
> >
> > Index: usb-2.6/drivers/usb/core/message.c
> > ===================================================================
> > --- usb-2.6.orig/drivers/usb/core/message.c
> > +++ usb-2.6/drivers/usb/core/message.c
> > @@ -323,8 +323,13 @@ static void sg_complete(struct urb *urb)
> > /* on the last completion, signal usb_sg_wait() */
> > io->bytes += urb->actual_length;
> > io->count--;
> > - if (!io->count)
> > + if (!io->count) {
> > + if (status == -ECONNRESET) {
> > + printk(KERN_ERR "Delaying for test\n");
> > + mdelay(600);
> > + }
> > complete(&io->complete);
> > + }
> >
> > spin_unlock(&io->lock);
> > }
> >
>
> I did so today on 2.6.36-rc8, without your other patch. I was still unable to
> reproduce the bug. Forget the whole thing as unreproducible?

What I said above wasn't quite right. This won't help trigger the
oops, but it should trigger the line saying something like

ehci_hcd 0000:00:12.2: qh ffff880208f07af0 (#00) state 5

That's the real bug.

Alan Stern



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