Re: Linux 3.0 oopses when pulling a USB CDROM

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Fri, 2011-07-01 at 17:04 -0400, Alan Stern wrote:
> On Fri, 1 Jul 2011, James Bottomley wrote:
> 
> > On Fri, 2011-07-01 at 14:14 -0400, Dave Jones wrote:
> > > On Fri, Jul 01, 2011 at 10:05:31AM -0700, Andi Kleen wrote:
> > > 
> > >  > I found I can reliably crash a 3.0 system by pulling the
> > >  > USB cable of a mounted USB cdrom (or rather a USB device which
> > >  > has a builtin fake CD-ROM) 
> > >  > 
> > >  > I suspect it's a regression too.
> > > 
> > > We've been seeing a lot of similar bugs in Fedora since we pushed
> > > a 2.6.38.8 update.  Some of the traces are different, but some
> > > look to be the same as yours. (here's one for eg: https://bugzilla.redhat.com/show_bug.cgi?id=712830)
> > > 
> > > The common cause seems to be 'device went away'. So USB CD drives,
> > > USB memory sticks, and for some reason virtualbox shutdown.
> > 
> > I think it's something specific in the USB path.  I can't reproduce on
> > 3.0-rc5 with a SATA DVD hot unplug.  USB cc's added.
> 
> I just took a look at the Red Hat bugzilla entry mentioned above.  It 
> seems to be quite different from the issue addressed by the patch I 
> just posted -- a crash with invalid memory access rather than a lockdep 
> violation and hang of the khubd thread.
> 
> It's also notable that the stack dump in the bugzilla report doesn't 
> contain any functions in the USB subsystem.  Of course this doesn't 
> prove anything, but it is suggestive.
> 
> Evidently the sdev argument to scsi_prep_state_check() was NULL.  This
> looks like the problem that cropped up before, where q->queuedata was
> getting set to NULL while the queue was still in use.  I can't imagine
> how anything in usb-storage could have caused that.

Right ... the device release function has already been called, so it's
some type of refcounting cockup.  The fact that I can't reproduce with a
SATA unplug is what makes me think it might be USB specific ... of
course, that's not definitive.

James