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

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Message-ID: <496798FE.8030900@s5r6.in-berlin.de>
Date:	Fri, 09 Jan 2009 19:35:42 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Greg Kroah-Hartman <gregkh@...e.de>
CC:	Kay Sievers <kay.sievers@...y.org>, linux-kernel@...r.kernel.org,
	Jay Fenlason <fenlason@...hat.com>
Subject: post 2.6.28 regression: device_initialize() now sleeps, and may fail
 without recovery strategy

>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.

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.

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?
-- 
Stefan Richter
-=====-==--= ---= -=--=
http://arcgraph.de/sr/
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