linux-kernel - Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel

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Date:	Wed, 13 Aug 2008 10:01:13 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Huang Ying <ying.huang@...el.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>, Vivek Goyal <vgoyal@...hat.com>,
	mingo@...e.hu, linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock,
 0) in kernel_kexec()

On Wed, 13 Aug 2008, Andrew Morton wrote:
>
> We don't need to create that local.  I queued this:

No, please don't. 

Just don't take this whole patch-series until it's cleaned up. There is 
absolutely no excuse for using xchg as a locking primitive. Nothing like 
this should be queued anywhere, it should be burned and the ashes should 
be scattered over the atlantic so that nobody will ever see them again.

F*ck me with a spoon, if you have to use xchg() to do a trylock, why the 
hell isn't the unlock sequence then

	smp_mb();
	var = 0;

instead? Not that that's really right either, but at least it avoids the 
_ridiculous_ crap. The real solution is probably to use a spinlock and 
trylock/unlock.

		Linus
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