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    SubjectRe: init's children list is long and slows reaping children.
    Linus Torvalds <> writes:

    > On Fri, 6 Apr 2007, Oleg Nesterov wrote:
    >> Oops. I misread stop_machine(), it does kernel_thread(), not kthread_create().
    >> So "stopmachine" threads are all re-parented to init when the caller exits.
    >> I think it makes sense to set ->exit_state = -1 in stopmachine(), regadless
    >> of any other changes.
    > I agree that "->exit_state = -1" makes sense, but I disagree in that I
    > don't think it *matters*.
    > Most of the problematic kernel threads are long-running (as in "never
    > exit"). Things like eventd, khelper, migration-threads etc will have init
    > as their parent and never actually exit, so their ->exit_state doesn't
    > matter. What matters is that they are on the children list, so when you
    > have 1024 CPU's, and init has many thousand of these per-cpu threads as
    > its children, then the *user* threads (that do exit) will cause problems!
    > I'd almost prefer to just not add kernel threads to any parent process
    > list *at*all*.

    Oleg is coming from a different case where it was found that exiting kernel
    threads were causing problems for nash when nash was run as init in an
    initramfs. While I think that case is likely a user space bug because
    nash should check the pid from waidpid before assuming the process it
    was waiting for returned.

    I do think you can construct valid embedded cases where you can prove
    there that among the user space processes certain actions are safe
    when they exit that a spare kernel space thread could invalidate.

    It just happens that the exit signal of kernel threads just matters on
    the other end of system size.

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      Last update: 2007-04-06 19:39    [W:0.045 / U:26.520 seconds]
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