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Re: Early boot failures with kFreeBSD >= 10.0~svn248992



On Tue, 07 May 2013 22:15:07 +0200
Christoph Egger <christoph@debian.org> wrote:

> FWIW I've been seeing this with gcc-4.6 gcc-4.7 and clang -- that's
> the reason we still don't have a newer kfreebsd-10 upload in the
> archive. Thank you for starting to dig! This is also the reason we
> have no 9.1 in kfreebsd-9 at least in experimental -- all tries didn't
> boot. All on my Notebook (Thinkpad X220 -- Sandy Bridge I5)

Thanks, reassuring to know it's not just me. =)

I've just spent a while looking over some strace output from the KVM
guest process when this happens, and I don't see anything that looks
concerning. top indicates that the first child thread of the qemu-kvm
process (presumably the worker for vCPU 0) is using 100% CPU time, but
strace says it's in the middle of an ioctl call:

  [pid 28279] ioctl(11, 0xae80 <unfinished ...>

lsof tells me that fd 11 in this case is of type anon_inode.

As far as I can tell, this is normal for a KVM guest process. I tried
looking at a healthy guest on the same machine, and it's behaving in
the same way -- it looks like this ioctl is the way that KVM vCPUs wait
for something to do.

I think this is ultimately not an efficient means of investigation to
pursue, so I plan to drop it and go back to trial and error -- I'll add
more and more of the responsible function definition until it breaks,
and then we can point at a specific line of code.

I probably won't have time to do this until the weekend, but I'll post
back here when I have something more to add.

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