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Date: Tue, 29 Nov 2011 19:51:49 +0530
From: Amit Shah <amit.shah@redhat.com>
To: Miche Baker-Harvey <miche@google.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>, Greg Kroah-Hartman <gregkh@suse.de>,
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Subject: Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.
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Hi,

On (Mon) 28 Nov 2011 [15:40:41], Miche Baker-Harvey wrote:
> Amit,
> 
> You said that the work would be serialized "due to port additions
> being on work items on the same workqueue".  I'm not seeing that.

You leave a lot of questions unanswered.  What's your environment?
Are you hot-plugging ports?  Are you using qemu?  What's your command
line?

> I've double checked this by using a mutex_trylock in
> hvc_console::hvc_alloc(), and here's the relevant output from dmesg:
> 
> root@myubuntu:~# dmesg | grep MBH
> [3307216.210274] MBH: got hvc_ports_mutex
> [3307216.210690] MBH: trylock of hvc_ports_mutex failed
> [3307216.211143] MBH: got hvc_ports_mutex
> 
> This is in a system with two virtio console ports, each of which is a
> console.  I think if the VIRTIO_CONSOLE_CONSOLE_PORT message handling
> were actually being serialized, the trylock should never fail.

Agreed.

> What's the source of the serialization for the workqueue items?  At
> first reading it looks like the control_work_handler gets called for
> each virtio interrupt?

It all depends on how you add ports.  If you're using qemu, they
happen via the control work handler.

		Amit