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    SubjectRe: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
    On 11/12/2010 10:11 AM, Don Zickus wrote:
    > On Fri, Nov 12, 2010 at 09:55:53AM -0600, Jason Wessel wrote:
    >>> To answer your question, I doubt this patch series will change that
    >>> outcome if it is still broken.
    >> It was most definitely broken in 2.6.36->2.6.37-rc1. Randy Dunlap had
    >> pointed this out in a separate exchange that was not on LKML.
    > Can you clarify by what you mean by broken above? Was 2.6.36 good or bad?

    It was absolutely broken in 2.6.36 which I believe is where the new
    LOCKUP_DETECTOR changes were introduced.

    I tested 2.6.35 and it does not hard hang, but suffered from a different
    problem with a perf API change. The kgdb tests appear to loop and loop
    emitting endless streams of output in 2.6.35 and I already have that
    problem patched.

    At this point we have to get back to a working base line. At this point
    if you use 2.6.37-rc1 the last remaining problem is the perf + lockup
    detector callback eating the injected DIE_NMI event which is meant to
    enter the debugger.

    >> The symptom you would see looks like:
    >> ...kernel boot...
    >> Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
    >> serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
    >> 00:06: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
    >> brd: module loaded
    >> kgdb: Registered I/O driver kgdbts.
    >> kgdbts:RUN plant and detach test
    >> [...HARD HANG STARTS HERE...]
    >> The kernel is looping at that point waiting for the master kgdb cpu to
    >> have all the slaves join the debugger but it never happens because the
    >> perf callback chain which is used by the lockup detector eats the NMI
    >> IPI event. After the perf callback is processed perf returns
    >> NOTIFY_STOP so the notifier which brings the slave CPU into the debugger
    >> never fires.
    > Ok. We have code to handle extra spurious NMIs that is hard to accurately
    > determine if the NMI was for perf or someone else. This logic may still
    > need tweaking. What cpu are you running on? AMD/Intel? If Intel, then
    > core/core2/nehalem?

    In this case I just built a 32 bit kernel and ran it under kvm on a 64
    bit host. I can send you the .config separately.

    kvm -nographic -k en-us -kernel arch/x86/boot/bzImage -net user -net
    nic,macaddr=52:54:00:12:34:56,model=i82557b -append
    "console=ttyS0,115200 ip=dhcp root=/dev/nfs
    nfsroot= rw acpi=force UMA=1" -smp 2


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