Re: [PATCH] usb: hcd: get/put device and hcd for hcd_buffers()

['Greg Kroah-Hartman' <gregkh@linuxfoundation.org>]

On Mon, Dec 08, 2014 at 09:44:05AM +0000, David Laight wrote:
> From: Greg Kroah-Hartman
> > On Fri, Dec 05, 2014 at 09:03:57PM +0100, Sebastian Andrzej Siewior wrote:
> > > Consider the following scenario:
> > > - plugin a webcam
> > > - play the stream via gst-launch-0.10 v4l2src device=/dev/video0
> > > - remove the USB-HCD during playback via "rmmod $HCD"
> > >
> > > and now wait for the crash
> > 
> > Which you deserve, why did you ever remove a kernel module?  That's racy
> > and _never_ recommended, which is why it never happens automatically and
> > only root can do it.
> 
> Really drivers and subsystems should have the required locking (etc) to
> ensure that kernel modules can either be unloaded, or that the unload
> request itself fails if the device is busy.
> 
> It shouldn't be considered a 'shoot self in foot' operation.
> OTOH there are likely to be bugs.

This is not always the case, sorry, removing a kernel module is a known
racy condition, and sometimes adding all of the locking required to try
to make it "safe" just isn't worth it overall, as this is something that
_only_ a developer does.

greg k-h