linux-kernel - Re: [PATCH 2/8] driver-core: add asynchronous probing support for drivers

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Date:	Wed, 8 Jul 2015 17:43:23 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...e.com>, Tom Gundersen <teg@...m.no>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Olof Johansson <olof@...om.net>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH 2/8] driver-core: add asynchronous probing support for drivers

On Mon, Jul 6, 2015 at 4:38 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Sat, Jul 04, 2015 at 07:09:19AM -0700, Dan Williams wrote:
>> The problem I ran into was needing to remove devices that still had
>> yet to be probed and not being able to use registration completion vs
>> the device_lock() to effectively synchronize the sub-system.
>
> Why do you need to "synchronize the sub-system"? The asynchronous
> probing should be transparent to the driver. Just unregister the device
> (or the driver) and driver core will ensure that probe() is not in
> flight.

Async registration is indeed transparent to the driver.  The primary
need to "flush registration" is the case of "region" devices that
reference a set of NVDIMM devices.  A region device requires all
related NVDIMMs to be active before the region can be enabled.

I'll look into a more concrete example of the tradeoffs between
asynchronous probing vs registration.
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