linux-kernel - Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

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Date:	Tue, 29 Nov 2011 19:51:49 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Miche Baker-Harvey <miche@...gle.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	Mike Waychison <mikew@...gle.com>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Eric Northrup <digitaleric@...gle.com>
Subject: Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

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@...buntu:~# 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
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