Re: 2.6.18-rc3-g3b445eea BUG: warning at/usr/src/linux-git/kernel/cpu.c:51/unlock_cpu_hotplug()

From: Jan Beulich
Date: Mon Aug 07 2006 - 04:15:30 EST

>> It's a false-positive in this case - the backtrace was complete. It would
>> be good if we could make the did-we-get-stuck detector a bit smarter. Even
>> special-casing "sysenter_past_esp" would stop a lot of this..
>Actually it's not completely false in this case -- it should
>have reached user mode and stopped there, but for some reason
>I didn't and already stopped still in the kernel.
>Most likely the CFI annotation for that sysenter path is not complete.

Correct, the return point of sysexit (SYSENTER_RETURN) is still in kernel space,
but its annotations are invisible to the unwinder. We should make the VDSO be
treated as user-mode code despite living above PAGE_OFFSET.

>It's on my todo list to investigate but I still hope Jan does it first ;-)

I'll try to, once I've got through moving the Xen code from 2.6.16 to 2.6.18-rc3

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