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From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>, Pavel Machek <pavel@ucw.cz>,
       nigel@nigel.suspend2.net, "Rafael J. Wysocki" <rjw@sisk.pl>,
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References: <1218618760.24951.137.camel@caritas-dev.intel.com>
	<alpine.LFD.1.10.0808130956360.3462@nehalem.linux-foundation.org>
Date: Wed, 13 Aug 2008 11:12:48 -0700
In-Reply-To: <alpine.LFD.1.10.0808130956360.3462@nehalem.linux-foundation.org>
	(Linus Torvalds's message of "Wed, 13 Aug 2008 09:57:33 -0700 (PDT)")
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Subject: Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel_kexec()
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Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Wed, 13 Aug 2008, Huang Ying wrote:
>>
>> -	xchg(&kexec_lock, 0);
>> +	locked = xchg(&kexec_lock, 0);
>> +	BUG_ON(!locked);
>
> Why do you want to do this at all? 
>
> And why do you implement your locks with xchg() in the first place? That's 
> total and utter crap.
>
> Hint: we have _real_ locking primitives in the kernel.

This part certainly.

The way the code should work, and the way it has in the past is:
image = xchg(&kexec_image, NULL)
if (!image)
   return -EINVAL;

Very simple and very obvious and very easy to get right, and it has
been that way for years.

Eric