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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 4 Jul 2015 07:09:19 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	Tom Gundersen <teg@...m.no>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	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 Fri, Jul 3, 2015 at 11:30 AM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
> On Sat, Jun 27, 2015 at 04:45:25PM -0700, Dan Williams wrote:
>> On Mon, Mar 30, 2015 at 4:20 PM, 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.
>> >
>> > Note that the end goal is to make the probing asynchronous by default,
>> > so annotating drivers with PROBE_PREFER_ASYNCHRONOUS is a temporary
>> > measure that allows us to speed up boot process while we validating and
>> > fixing the rest of the drivers and preparing userspace.
>> >
>> > This change is based on earlier patch by "Luis R. Rodriguez"
>> > <mcgrof@...e.com>
>> >
>> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>> > ---
>> >  drivers/base/base.h    |   1 +
>> >  drivers/base/bus.c     |  31 +++++++---
>> >  drivers/base/dd.c      | 149 ++++++++++++++++++++++++++++++++++++++++++-------
>> >  include/linux/device.h |  28 ++++++++++
>> >  4 files changed, 182 insertions(+), 27 deletions(-)
>>
>> Just noticed this patch.  It caught my eye because I had a hard time
>> getting an open coded implementation of asynchronous probing to work
>> in the new libnvdimm subsystem.  Especially the messy races of tearing
>> things down while probing is still in flight.  I ended up implementing
>> asynchronous device registration which eliminated a lot of complexity
>> and of course the bugs.  In general I tend to think that async
>> registration is less risky than async probe since it keeps wider
>> portions of the traditional device model synchronous
>
> but its not see -DEFER_PROBE even before async probe.

Except in that case you know probe has been seen by the driver at
least once.  So I see that as less of a surprise, but point taken.

>> and leverages the
>> fact that the device model is already well prepared for asynchronous
>> arrival of devices due to hotplug.
>
> I think this sounds reasonable, do you have your code upstream or posted?

Yes, see nd_device_register() in drivers/nvdimm/bus.c

> If not will you be at Plumbers?

Yes.

> Maybe we shoudl talk about this as although
> ChromeOS already likely already jumped on async probe we should address a
> way forward and path forward for other distributions and I don't think anyone
> is looking too much into it. async probe came to Linux for two reasons:
>
>  * chromeos wanting it
>  * an incorrect systemd assumption on how the driver core works
>
> So long term we still need to address the systemd approach, are they going
> to be defaulting now to async probe for all modules? How about for built-ins?
>
> We should talk about this and maybe at plumbers.
>
>> Splitting the "initial probe" from
>> the "manual probe" case seems like a recipe for confusion.
>
> If you can come up with pros / cons on both strategies it'd be
> valuable.

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/