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    SubjectRe: 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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