Re: Null Pointer BUG in uhci_hcd

Alan Stern
2009-07-09T14:19:13Z

On Wed, 8 Jul 2009, Michael S. Zick wrote:

> It is unlikely that VIA Tech. will recall the CX700 chipset.
>
> So being able to take a device off-line (like the driver claims it is doing)
> and *leave* it off-line - until told to "try again" - that would be an
> improvement.

Sorry, you lost me there. In all the logs you have posted, I can find
only one line where the kernel claims to be taking a device offline:

> Jun 30 10:38:31 cb01 kernel: sd 2:0:0:0: Device offlined - not ready after error recovery

And in that case it _did_ leave the device offline. So what are you
concerned about?

> The current process of filling up the /var/log directory until the machine
> chokes is a rather fragile sort of response to a hot-plugged device, good or bad.

It isn't a response to a hot-plugged device; it's a response to broken
hardware. If your hardware was working properly you could hot-plug
and hot-unplug devices 'till you turned blue in the face, without
filling up the /var/log directory.

> > > > I suspect it's worse than a simple interrupt-routing mistake.
> > > >
> > >
> > > I would not object to your removing that one mistake - that is one less
> > > to contend with.
> >
> > I didn't say there was an interrupt-routing mistake; I said it was
> > _worse_ than an interrupt-routing mistake.
> >
>
> Never claimed you did - the driver made that claim.
> But still, it would be nice to get rid of the interrupt-routing mistake.

How can you get rid of an interrupt-routine mistake if there is no such
mistake in the first place?

Not that I'm claiming there is no such mistake -- the logs you have
provided aren't clear in this respect. So that's the first issue to
address: Determine whether the interrupts are or aren't being routed
correctly.

To that end, you should try doing some more directed testing.

Start with a nice cold boot, with no USB devices plugged in. Copy the
dmesg log and clear the kernel's log buffer. And just to get as much
information as possible, start a process copying usbmon's 0u file
(you'll have to enable CONFIG_USB_MON if it isn't already enabled).

Then plug in a high-speed device. When everything settles down, copy
the dmesg buffer again and also get a copy of the
/sys/kernel/debug/ehci/0000:00:10.4/registers file. Those, together
with the usbmon trace, will provide a good starting point.

Assuming something goes wrong, of course. If everything works okay,
you'll have to keep trying similar experiments (plugging and unplugging
devices) until something breaks.

Alan Stern