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

[Andi Kleen <ak@muc.de>]

> >  [<c0171577>] vfs_write+0xcd/0x179
> >  [<c0171c20>] sys_write+0x3b/0x71
> >  [<c010318d>] sysenter_past_esp+0x56/0x8d
> This "unwinder stuck" thing seems to be very common.

Yes, there are still a lot of bugs in the unwind annotation
unfortunately.

We're also slowly discovering that some things we do cannot
even be expressed in CFI, so some code has to change.

> 
> 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.

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

-Andi


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