linux-kernel - Re: Linux 3.0 oopses when pulling a USB CDROM

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Date:	Fri, 1 Jul 2011 22:03:31 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
cc:	Dave Jones <davej@...hat.com>, Andi Kleen <andi@...stfloor.org>,
	<linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<axboe@...nel.dk>, <rjw@...k.pl>, <linux-usb@...r.kernel.org>
Subject: Re: Linux 3.0 oopses when pulling a USB CDROM

On Fri, 1 Jul 2011, James Bottomley wrote:

> 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.

I'm not able to reproduce it on a vanilla 3.0-rc5 system.  Can anybody
give the exact sequence of steps you went through to trigger the bug?

Alan Stern

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