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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Thu, 27 Aug 2009 19:27:23 +1000
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Subject: [Qemu-devel] Re: Extending virtio_console to support multiple ports
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To: Alan Cox <alan@linux.intel.com>
Cc: kvm@vger.kernel.org, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, miltonm@bga.com, qemu-devel@nongnu.org, borntraeger@de.ibm.com, brueckner@linux.vnet.ibm.com, Amit Shah <amit.shah@redhat.com>, virtualization@lists.linux-foundation.org

On Thu, 2009-08-27 at 10:08 +0100, Alan Cox wrote:
> >  - Then, are we certain that there's no case where the tty layer will
> > call us with some lock held or in an atomic context ? To be honest,
> > I've totally lost track of the locking rules in tty land lately so it
> > might well be ok, but something to verify.
> 
> Some of the less well behaved line disciplines do this and always have
> done.

That was also my understanding but heh, I though that maybe you may have
fixed all of that already :-)

So at this stage, I think the reasonably thing to do is to stick to the
spinlock, but we can try to make it a bit smarter, and we can definitely
attempt to fix the case Amit pointed out where we call resize without a
lock while it seems to expect it (though we also need to be careful
about re-entrancy I believe).

Cheers,
Ben.