linux-kernel - Re: uses of cmpxchg/xadd in spinlock.h and rwsem.h vs. CONFIG

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Message-ID: <20090512153732.GA31131@wotan.suse.de>
Date:	Tue, 12 May 2009 17:37:32 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: uses of cmpxchg/xadd in spinlock.h and rwsem.h vs. CONFIG_M386

On Tue, May 12, 2009 at 04:19:00PM +0100, Jan Beulich wrote:
> While looking at a completely different issue I happened to grep for uses of
> xadd, and it would appear to me that there got uses added that would make
> a M386-configured SMP kernel die on an actual i386.
> 
> Oh, for the rwsem case I see - it would use the RWSEM_GENERIC_SPINLOCK case
> when selecting M386. But I see nothing similar for the ticket spinlocks - am
> I overlooking something?

Oh, hmm, we do actually attempt to support 386 SMP kernels... I thought
that config wasn't allowed, but looking at the atomic.h code, it has
ifdef fallbacks.

I guess some similar hacks could be added to spinlock.h code.
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