Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common

[Eric Dumazet]

Le samedi 13 novembre 2010 Ã 18:17 +0800, AmÃrico Wang a Ãcrit :
> 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.

cmpxchg() is a full memory barrier, no need for smp_wmb() or barrier()



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