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    SubjectRe: [tip: sched/urgent] sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU

    * tip-bot2 for Oleg Nesterov <tip-bot2@linutronix.de> wrote:

    > Another corner case is "nohz_full=0" on a machine with a single CPU or with
    > the maxcpus=1 kernel argument. In this case non_housekeeping_mask is empty
    > and tick_nohz_full_setup() makes no sense. And indeed, the kernel hits the
    > WARN_ON(tick_nohz_full_running) in tick_sched_do_timer().
    >
    > And how should the kernel interpret the "nohz_full=" parameter? It should
    > be silently ignored, but currently cpulist_parse() happily returns the
    > empty cpumask and this leads to the same problem.
    >
    > Change housekeeping_setup() to check cpumask_empty(non_housekeeping_mask)
    > and do nothing in this case.

    So arguably the user meant NOHZ_FULL to be turned off - but it is de-facto
    already turned off by the fact that there's only a single CPU available,
    right?

    Thanks,

    Ingo

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