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    SubjectRe: CONFIG_PREEMPT_RCU in next/mmotm
    On Sun, 9 Aug 2009, Hugh Dickins wrote:
    >
    > filp 13343 objects:
    >
    > CPU last cur F M
    > 0 1 0 0 0
    > 1 0 0 0 0
    > 2 -1 0 0 0
    > 3 0 0 0 0
    > ggp = 35124, state = waitzero

    Interesting that rcu_try_flip_waitzero() doesn't see 1 + 0 + -1 + 0 == 0.

    That's because rcu_cpu_online_map is 0x1 instead of the 0xf it should be.

    Which is because I don't have CONFIG_HOTPLUG_CPU=y on that PPC machine
    (unlike the x86s), and I think you've made some recent mods which
    accidentally made the rcu cpu initialization dependent on hotplug
    cpu notifiers? CONFIG_HOTPLUG_CPU=y and it works properly again.

    And TREE_RCU doesn't use an rcu_cpu_online_map (though it does expect
    some per-cpu initialization, but seems to get away without it).

    So I think that's the mystery solved - I'll let you decide the right fix!

    Hugh


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