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

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Message-ID: <20150706234146.GH32140@dtor-ws>
Date:	Mon, 6 Jul 2015 16:41:46 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Tomeu Vizoso <tomeu.vizoso@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Luis R . Rodriguez" <mcgrof@...e.com>, Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <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, Jun 01, 2015 at 02:04:01PM +0200, Tomeu Vizoso wrote:
> On 29 May 2015 at 15:23, Tomeu Vizoso <tomeu.vizoso@...il.com> wrote:
> > On 29 May 2015 at 12:48, Tomeu Vizoso <tomeu.vizoso@...il.com> wrote:
> >> On 31 March 2015 at 01:20, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> >>> Some devices take a long time when initializing, and not all drivers are
> >>> suited to initialize their devices when they are open. For example,
> >>> input drivers need to interrogate their devices in order to publish
> >>> device's capabilities before userspace will open them. When such drivers
> >>> are compiled into kernel they may stall entire kernel initialization.
> >>>
> >>> This change allows drivers request for their probe functions to be
> >>> called asynchronously during driver and device registration (manual
> >>> binding is still synchronous). Because async_schedule is used to perform
> >>> asynchronous calls module loading will still wait for the probing to
> >>> complete.
> >>
> >> But what about parents? Don't we need to make sure that before probing
> >> a device its parent has finished probing already?
> >
> > Have realized that this is an existing problem that was just made more
> > probable by async probe, as before async probing the parent could have
> > deferred its probe and then its children would be probed.
> >
> > Wonder if drivers should be modified to defer its probe if their
> > parent isn't probed yet, or if we can codify that in dd.c.
> 
> Also wonder what's the plan regarding USB interfaces requiring that
> their parent's lock is taken before probing.

Yes, indeed, we need to take paren's lock in async probe too. I'll make
a patch.

Thanks for spotting this.

-- 
Dmitry
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