linux-kernel - Re: post 2.6.28 regression: device_initialize() now sleeps, and may fail without recovery strategy

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Date:	Fri, 9 Jan 2009 12:56:33 -0800
From:	Greg KH <gregkh@...e.de>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Kay Sievers <kay.sievers@...y.org>, linux-kernel@...r.kernel.org,
	Jay Fenlason <fenlason@...hat.com>
Subject: Re: post 2.6.28 regression: device_initialize() now sleeps, and
	may fail without recovery strategy

On Fri, Jan 09, 2009 at 07:35:42PM +0100, Stefan Richter wrote:
> >From commit 2831fe6f9cc4e16c103504ee09a47a084297c0f3, "driver core:
> create a private portion of struct device":
> 
>  void device_initialize(struct device *dev)
>  {
> +	dev->p = kzalloc(sizeof(*dev->p), GFP_KERNEL);
> +	if (!dev->p) {
> +		WARN_ON(1);
> +		return;
> +	}
> +	dev->p->device = dev;
>  	dev->kobj.kset = devices_kset;
>  	kobject_init(&dev->kobj, &device_ktype);
> 
> 
> First of all, this prevents initialization of struct device in atomic
> contexts, such as drivers/firewire/fw-device.c::fw_node_event.

Ick, sorry, I didn't think that any callers ever did this.

> This is a bug in current mainline.
> 
> We can fix the bug by changing firewire-core, but
>   a) it'd be more than a one-liner,
>   b) who knows which other subsystems are affected.

I agree.

I originally looked at changing this to be at device_add time, but I
think there are some code paths that do device_initialize and then do
some operations on the device before calling device_add.  But I could be
wrong, let me do some testing first before forcing you to make that big
change to the firewire core.

> Next, the above code is bogus.  In 2.6.28, device_initialize() could
> never fail and was thus safe to use as a void-valued function.
> 
> How does driver core handle dev->p == NULL in subsequent usages of dev now?

It dies a flaming horrible death, pretty much like the whole rest of the
system if allocating such a small ammount of memory is causing failures
:)

Give me a few hours to test here, your change might not be necessary...

thanks,

greg k-h
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