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    SubjectRe: calling smp_call_function_many() with non-stable CPU mask
    Date
    > There are a couple of examples of smp_call_function_many() getting
    > called with mm_cpumask() as the first argument. Since that mask
    > generally can change while smp_call_function_many() is executing,
    > it seems there might be a problem with the case where that mask
    > becomes empty after the initial checks, but before the mask is made
    > permanent (by copying into data->cpumask).
    >
    > Shouldn't there be a check of data->refs being zero right after
    > setting it (to avoid having csd_lock_wait() wait for a remote CPU
    > to clear the lock flag, and to avoid adding the entry to
    > call_function.queue)?
    >
    > If that isn't considered necessary, is it then incorrect to pass
    > in-flight CPU masks to smp_call_function_many() (and should
    > this requirement then be documented somewhere, and the
    > existing calls all be inspected for correctness)?
    >

    Mike Galbraith just brought this up, and I supplied a patch, and even
    a rediff on top of other changes:

    http://lkml.indiana.edu/hypermail/linux/kernel/1101.3/02813.html
    http://lkml.indiana.edu/hypermail/linux/kernel/1101.3/03172.html

    http://lkml.indiana.edu/hypermail/linux/kernel/1102.0/00017.html


    This doesn't address https://bugzilla.kernel.org/show_bug.cgi?id=23042
    which is x86 not expecting the mask to be cleared while its thinking
    about the mask.

    milton


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