Re: [PATCH 08/10] virtio: console: add locks around buffer removal in port unplug path

[Amit Shah <amit.shah@redhat.com>]

On (Mon) 22 Jul 2013 [15:26:22], Rusty Russell wrote:
> Amit Shah <amit.shah@redhat.com> writes:
> > The removal functions act on the vqs, and the vq operations need to be
> > locked.
> >
> > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> 
> How can userspace access the port now?  By the time we are cleaning up
> buffers, there should be no possibility of such accesses.

close(), can happen when the port is being unplugged.  We're just
making sure here that port_fops_release() and unplug_port() don't try
to free up the same data at the same time.

> The number of bugfixes here is deeply disturbing.

Yes, the first three fix a bug - close() after unplug.  However, the
others are inadequate locking fixes which I noticed while fixing that
bug.

Port unplug isn't a frequently-used or tested path, so these were
lying unnoticed so far.

>  I wonder if it's be
> easier to rewrite it all with a lock per port, and one global to protect
> ports_driver_data.

Hm, with this series, I don't see anything that might need extra
locking.  Though I'll take a look at this afresh in a while -- and see
if we could simplify something.

Given that this was necessary only for unplug operations, (and they
aren't a 'regular operation', so we could drop the stable@ for the
series?), are you OK with this series for now?

		Amit