linux-kernel - Re: [PATCH] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

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Date:	Tue, 24 Jun 2014 09:51:01 -0400
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, plagnioj@...osoft.com,
	tomi.valkeinen@...com, linux-fbdev@...r.kernel.org, olaf@...fle.de,
	apw@...onical.com, jasowang@...hat.com, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH] video: hyperv: hyperv_fb: refresh the VM screen by force
 on VM panic

On Tue, Jun 24, 2014 at 08:29:17AM +0800, Dexuan Cui wrote:
> Currently the VSC has no chance to notify the VSP of the dirty rectangle on VM
> panic because the notification work is done in a workqueue, and in panic() the
> kernel typically ends up in an infinite loop, and a typical kernel config has
> CONFIG_PREEMPT_VOLUNTARY=y and CONFIG_PREEMPT is not set, so a context switch
> can't happen in panic() and the workqueue won't have a chance to run. As a
> result, the VM Connection window can't refresh until it's closed and we
> re-connect to the VM.
> 
> We can register a handler on panic_notifier_list: the handler can notify
> the VSC and switch the framebuffer driver to a "synchronous mode", meaning
> the VSC flushes any future framebuffer change to the VSP immediately.
> 
> MS-TFS: 157532

What is this line for?

thanks,

greg k-h
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