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    SubjectRe: [PATCH 4/5] kgdb: Use atomic operators which use barriers
    On Fri, Apr 02, 2010 at 04:24:57PM -0700, Linus Torvalds wrote:
    >
    >
    > On Fri, 2 Apr 2010, Russell King - ARM Linux wrote:
    > >
    > > Actually, in future threads you end up agreeing with my position...
    >
    > I always agreed that it was not a memory barrier.
    >
    > In fact, the commit that extended on the "volatile-considered-harmful"
    > patch from you has this quote from me in the commit logs:
    >
    > Linus sayeth:
    >
    > : I don't think it was ever the intention that it would be seen as anything
    > : but a compiler barrier, although it is obviously implied that it might
    > : well perform some per-architecture actions that have "memory barrier-like"
    > : semantics.
    > :
    > : After all, the whole and only point of the "cpu_relax()" thing is to tell
    > : the CPU that we're busy-looping on some event.
    > :
    > : And that "event" might be (and often is) about reading the same memory
    > : location over and over until it changes to what we want it to be. So it's
    > : quite possible that on various architectures the "cpu_relax()" could be
    > : about making sure that such a tight loop on loads doesn't starve cache
    > : transactions, for example - and as such look a bit like a memory barrier
    > : from a CPU standpoint.
    > :
    > : But it's not meant to have any kind of architectural memory ordering
    > : semantics as far as the kernel is concerned - those must come from other
    > : sources.
    >
    > which I think is pretty clear.
    >
    > But that quote seems to be the one where you then think I "agree" with
    > you.

    Yet again you read something into what I say that wasn't there.

    Wait for me to return from holiday, as I said, and I'll respond further.


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