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    SubjectRe: [PATCH RFC] panic: Avoid extra noisy messages due to stopped cpus
    On Thu, Oct 11, 2018 at 03:17:48PM +0800, Feng Tang wrote:
    > Sometimes when debugging kernel panic, we saw many extra noisy error
    > messages after the expected end:
    >
    > [ 35.743249] ---[ end Kernel panic - not syncing: Fatal exception
    > [ 35.749975] ------------[ cut here ]------------
    >
    > These messages may overflow the sceen (framebuffer) and make debugging
    > much difficulter.

    *blink* you actually using the framebuffer for debugging ?! Why the heck
    are you doing that?

    > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
    > index c93fcfd..b703862 100644
    > --- a/arch/x86/kernel/process.c
    > +++ b/arch/x86/kernel/process.c
    > @@ -520,6 +520,7 @@ void stop_this_cpu(void *dummy)
    > * Remove this CPU:
    > */
    > set_cpu_online(smp_processor_id(), false);
    > + set_cpu_active(smp_processor_id(), false);
    > disable_local_APIC();
    > mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
    >

    WTH is stop_this_cpu() and how do we even get here with active still
    set?

    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 7fc4a37..cf41b7b 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -9034,7 +9034,7 @@ static inline int find_new_ilb(void)
    > {
    > int ilb = cpumask_first(nohz.idle_cpus_mask);
    >
    > - if (ilb < nr_cpu_ids && idle_cpu(ilb))
    > + if (ilb < nr_cpu_ids && idle_cpu(ilb) && cpu_online(ilb))
    > return ilb;
    >
    > return nr_cpu_ids;


    Similar, this is the result of taking the CPU away without going through
    the normal path. You're doing something dodgy.

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