linux-kernel - Re: [PATCH] driver core: fix shutdown races with probe/remove

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Date:	Tue, 5 Jun 2012 17:38:39 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] driver core: fix shutdown races with probe/remove

Hi,

On Tue, Jun 5, 2012 at 5:18 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Jun 05, 2012 at 04:59:07PM +0800, Ming Lei wrote:
>> Firstly, .shutdown callback may touch a uninitialized hardware
>> if dev->driver is set and .probe is not completed.
>
> When would that ever happen?

It may happen when someone plugs a device, then run 'shutdown' immediately.

>
>> Secondly, device_shutdown() may dereference a null pointer to cause
>> oops when dev->driver is cleared after it is checked in device_shutdown().
>
> Again, when would that happen?  A new device/driver being added to the
> system as it is being shutdown?

It is usually that someone presses 'power off' button and unplugs
its usb devices or pci/e devices, maybe together with a new plug.

In such case, the oops may be triggered.

>
> Has anyone ever hit that before?

Looks someone has reported it, I also can trigger it
with some delay added in device_shutdown.

>
> Is this really needed?

In case that it is triggered, oops will prevent system from being
shutdown, and it should be a big problem.

IMO, we can avoid it without much change and side effect, so
looks worthy the change.

Thanks,
--
Ming Lei
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