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    SubjectRe: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep
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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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