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Date: Tue, 13 Aug 2013 13:04:01 +0100
From: "Richard W.M. Jones" <rjones@redhat.com>
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Errors-To: user-mode-linux-devel-bounces@lists.sourceforge.net
Subject: Re: [uml-devel] How to reliably kill all vmlinux processes for a
 single VM?
To: Richard Weinberger <richard@nod.at>
Cc: "user-mode-linux-devel@lists.sourceforge.net" <user-mode-linux-devel@lists.sourceforge.net>


OK, I understand what's going wrong and how to reproduce the
signal-to-parent problem.  It does look like a bug in vmlinux.

It happens if the init process (PID 1) inside the VM gets a segfault.

In libguestfs we can force that easily, as there is a test path for
exercising segfaults in our init process:

----------------------------------------------------------------------
#!/bin/bash -
export LIBGUESTFS_BACKEND=uml
export LIBGUESTFS_QEMU=/home/rjones/d/linux/vmlinux
export LIBGUESTFS_DEBUG=1
export LIBGUESTFS_TRACE=1
./run strace -o /tmp/strace.log ./fish/guestfish -a /dev/null <<EOF
run
get-pid
debug segv 1
!sleep 5
EOF
----------------------------------------------------------------------

The output of this and the strace log file is here:

http://oirase.annexia.org/tmp/uml-signal/

output.log.txt shows the PID of vmlinux is 6856.

strace.log.txt shows that the parent process gets terminated by
SIGTERM *from* PID 6856:

--- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=6856, si_uid=1000} ---
+++ killed by SIGTERM +++

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

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