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    Subject[PATCH 0/6] sched: TTWU, IPI, and assorted stuff
    Hi,

    So Paul reported rcutorture hitting a NULL dereference, and patch #1 fixes it.

    Now, patch #1 is obviously correct, but I can't explain how exactly it leads to
    the observed NULL pointer dereference. The NULL pointer deref happens in
    find_matching_se()'s last while() loop when is_same_group() fails even though
    both parents are NULL.

    The only explanation I have for that is that we just did an activate_task()
    while: 'task_cpu(p) != cpu_of(rq)', because then 'p->se.cfs_rq' doesn't match.
    However, I can't see how the lack of #1 would lead to that. Never-the-less,
    patch #2 adds assertions to warn us of this case.

    Patch #3 is a trivial rename that ought to eradicate some confusion.

    The last 3 patches is what I ended up with for cleaning up the whole
    smp_call_function/irq_work/ttwu thing more.

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