linux-kernel - Re: [PATCH 08/23] clocksource: drop duplicate register checking

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Message-ID: <20070131095935.GA22377@elte.hu>
Date:	Wed, 31 Jan 2007 10:59:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, johnstul@...ibm.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 08/23] clocksource: drop duplicate register checking


* Daniel Walker <dwalker@...sta.com> wrote:

> This is something Thomas already dropped, [...]

(i think you forgot to Cc: Thomas here, nor is this something that 
Thomas' change dropped.)

> [...] and I'm just sticking with that .. If you register your 
> clocksource _twice_ your kernel will likely not work correctly (and 
> might crash).

this is a quite bad change. John's original clocksource code protects 
against double registry:

         if (is_registered_source(c)) {
                 printk("register_clocksource: Cannot register %s. "
                        "Already registered!", c->name);
                 ret = -EBUSY;

and Thomas' change keeps that property, but doesnt printk. Your change 
makes double registry possible, potentially crashing the kernel later 
on! (And this isnt theoretical, double registry did happen in practice 
when i debugged suspend problems on my SMP laptop.)

	Ingo
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