linux-kernel - Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin

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Date:	Sat, 13 Nov 2010 18:17:32 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common

On Wed, Nov 03, 2010 at 10:59:47AM -0400, Jeremy Fitzhardinge wrote:

>+	union {
>+		struct __raw_tickets tickets;
>+		__ticketpair_t slock;
>+	} tmp, new;
>+	int ret;
>+
>+	tmp.tickets = ACCESS_ONCE(lock->tickets);
>+	if (tmp.tickets.head != tmp.tickets.tail)
>+		return 0;
>+
>+	new.slock = tmp.slock + (1 << TICKET_SHIFT);
>+
>+	ret = cmpxchg(&lock->ticketpair, tmp.slock, new.slock) == tmp.slock;
>+	barrier();		/* just make nothing creeps before lock is claimed */

This one should be smp_wmb(), right? No CONFIG_X86_OOSTORE protected.
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