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

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

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()




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel