Bug#844498: disorderfs: using it for building kills the host (with a 686 kernel)

[Holger Levsen]

Package: disorderfs
Version: 0.5.1-1
Severity: normal

Hi,

so we had disorderfs disabled for a long time on our reproducible setup
and yesterday I enabled it again for i386 only, which rather immediatly
caused profitbricks-build2-i386.debian.net to hang/die… so I rebootet it
and logged in to investigate…

and while watched diskspace… and suddenly the host was "gone". I observed this
as I typed "ps fax|grep wesnot" in another shell. Also Trying to ssh in resulted 
in this:

$ ssh profitbricks-build2-i386.debian.net 
Last login: Wed Nov 16 10:14:27 2016 from …

and hangs there.

So "killing the host" means: the kernel and processes are still running but
are stuck on io, eg I had "watch df" running in an ssh session, it was
not updating anymore but I could ctrl-c it and get back to the shell
prompt. as soon as i pressed enter on a command, it hung.

Interesting, disorderfs was used on two hosts, but this only happened on pb2,
but not pb6! pb2 is running 3.16.0-4-686-pae while pb6 is running 3.16.0-4-amd64
(and both run i386 userland).

Thogh it's unclear whether it would not also "kill" pb6 if we were using it
long enough.

Also, using disorderfs for a few jobs seems to be fine, but there are 8 pbuilder
jobs running simultaenously on each of these hosts and half of them are using
disorderfs.

Next easy tests:
- enable disorderfs on some armhf hosts (running 32bit kernels too)
- upgrade pb2 to a 4.7 bpo 686 kernel
- eneable disorderfs on amd64


-- 
cheers,
	Holger
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