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

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Date:	Tue, 12 May 2009 18:02:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Jan Beulich <JBeulich@...ell.com>, 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, 2009-05-12 at 17:37 +0200, Nick Piggin wrote:
> 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.

Last time this came up I thought we decided i386-smp wasn't supported,
and the Kconfig files ought to be adjusted.
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