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    SubjectRe: [PATCH] sound_core.c: Remove BKL from soundcore_open
    On Sun, 11 Oct 2009 09:20:15 -0600
    Jonathan Corbet <corbet@lwn.net> wrote:

    > Changing the
    > BKL to a mutex is a real semantic change which requires a real survey
    > of the code affected.

    One other aspect of this I forgot to mention...it's actually possible
    (if unlikely) that one of those lower-level open routines depends on
    the BKL's release-on-sleep semantics. Swapping in a mutex would change
    that behavior, possibly resulting in deadlocks.

    I think it was Alan who once pointed out that the BKL is badly
    misnamed. It isn't really a lock, it's a modified execution
    environment designed to let naive kernel code think it's still running
    in a uniprocessor, no-preemption situation. Replacing the BKL with a
    different lock changes that environment, so one has to be *really*
    careful about looking for any assumptions which may remain in the code.

    That's why BKL-hunting is harder than it looks - and why the BKL has
    hung around for all these years.

    jon


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