Messages in this thread | | | Subject | Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep | From | Peter Zijlstra <> | Date | Fri, 22 Feb 2008 14:40:54 +0100 |
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On Fri, 2008-02-22 at 08:35 -0500, Steven Rostedt wrote:
> > My assumption is that the xchg() (inside update_current()) acts as an > > effective wmb(). If xchg() does not have this property, then this code > > is broken and patch 6/14 should also add a: > > > > > > + smp_wmb(); > > I believe that the wmb would be needed. I doubt that xchg on all archs > would force any ordering of reads and writes. It only needs to guarantee the > atomic nature of the data exchange. I don't see any reason that it would > imply any type of memory barrier.
Documentation/memory-barriers.txt states:
Any atomic operation that modifies some state in memory and returns information about the state (old or new) implies an SMP-conditional general memory barrier (smp_mb()) on each side of the actual operation (with the exception of explicit lock operations, described later). These include:
xchg();
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