linux-kernel - Re: Null Pointer BUG in uhci

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Message-ID: <Pine.LNX.4.44L0.0907081658260.22105-100000@iolanthe.rowland.org>
Date:	Wed, 8 Jul 2009 17:02:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Michael S. Zick" <lkml@...ethan.org>
cc:	Oliver Neukum <oliver@...kum.org>, Jiri Kosina <jkosina@...e.cz>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: Null Pointer BUG in uhci_hcd

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

> > Like I've been telling you all along, the hardware isn't working.  
> >
> 
> That sounds very fragile.

I'm not sure how to interpret that sentence.  If you mean that your
system's hardware design isn't good, I agree.  If you mean that the
kernel shouldn't produce a lot of output when faced with broken
hardware, that's not so clear.  What else should it do (bearing in mind
that the kernel can't tell the hardware is broken)?

> > 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.

> > > > > For more information enable CONFIG_USB_DEBUG and CONFIG_DEBUG_FS, then 
> > > > > see what's sitting in the usb/uhci/* files in debugfs.
> > > > > 
> > > 
> 
> Fours up-time - nothing written to dmesg since boot -
> Just the usual hard-lockup.
> 
> Also - something in the combined fix/diagnostic patch
> disable any sensing of external usb events.
> So I couldn't very well poke devices at it.  ;)

You should take out those BUG statements.  If they ever trigger, they 
will certainly lock up your system.

Alan Stern

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