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    SubjectRe: [patch 00/21] mutex subsystem, -V14

    On Thu, 5 Jan 2006, Ingo Molnar wrote:
    > [ long details removed ]
    > to sum it up: atomic_dec/inc_return() alone is not enough to implement
    > critical sections, on a number of architectures. atomic_xchg() seems to
    > have similar problems too.


    > the patch below adds the smp_mb() barriers to the generic headers, which
    > should now fulfill all the ordering requirements, on every architecture.
    > It only relies on one property of the atomic primitives: that they wont
    > get reordered with respect to themselves, so an atomic_inc_ret() and an
    > atomic_dec_ret() cannot switch place.
    > Can you see any hole in this reasoning?

    No. The alternative is to just make the ordering requirements
    for "atomic_dec_return()" and "atomic_xchg()" be absolute. Say that they
    have to be full memory barriers, and push the problem into the low-level

    I _think_ your patch is the right approach, because most architectures are
    likely to do their own fast-paths for mutexes, and as such the generic
    ones are more of a template for how to do it, and hopefilly aren't that
    performance critical.

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