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    SubjectRe: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs
    On Wed, 4 May 2011, Valdis.Kletnieks@vt.edu wrote:

    > On Wed, 04 May 2011 15:04:39 CDT, Christoph Lameter said:
    > > On Wed, 4 May 2011, Linus Torvalds wrote:
    >
    > > > But cmpxchg DOES NOT MAKE SENSE without atomicity guarantees.
    > >
    > > This is not a real cmpxchg after all. Its not atomic in the sense of
    > > other functions. Its only "percpu atomic" if you want it that way. This is
    > > *not* a full cmpxchg_double().
    >
    > Calling it a cmpxchg when it doesn't have the primary distinguishing property
    > of a hardware cmpxchg is just loading a bullet in the chamber and inviting
    > kernel hackers to point it at their feet...

    It does have most of the distinguishing characterstics but the
    lock-prefixless cmpxchg8b/16b (which is quite fast) is used in a
    unique way here in a percpu fastdpath. Thats why we have the strange
    naming this_cpu_cmpxchg_double etc.





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