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    SubjectRe: [PATCH v5 3/3] Add BUG_XX() debugging hard/soft lockup detection
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    > Because when you catch a bug in the hard lockup detector the system
    > just sits there hard hung and you are not able to get into a debugger
    > console since the system has crashed and the watchdog code has already
    > killed off the other processors and locked up all the NMI interrupt
    > handlers, thereby preventing any debugger at all from functioning
    > other than a hardware ice, so it's a hell of a lot easier just to
    > trigger a break when you detect the first instance of a hard lockup
    > before the system is completely hosed.
    >

    So this is why Ingo and tglx's suggestion doesn't work. Unless you
    can set a breakpoint in the detector coede, once the lockup occurs
    about 50% of the time (when the IF flag is not set and interrupts are
    disabled), you can't get into a debugger because the system is hosed.

    The way the current hard lockup detector works is a lot like the death
    star self-destruct system for linux -- it detects one, tries to IPI
    the other processors to dump their stacks, then somewhere down in the
    OS all of it locks up -- once and a while I can get it too panic. A
    great bug to test your detector with is the one in timekeeper.c tglx
    and I worked on. Good luck getting into any debugger when it fires
    off. I like the fact this code does not call panic and is somewhat
    dynamic allowing recovery of the system, but it takes a healthy system
    with a single bug, burns it to the ground, locks up all the
    processors, and prevents the debugger from being entered unless a
    breakpoint has been set.

    Perhaps this helps you understand.

    Jeff

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