Control: tags -1 upstream

David,

I know it has been a long time, but thanks for this.

On Mon, Jul 16, 2018 at 01:52:51AM +0200, David Kuehling wrote:
> Short summary of the problem: during shutdown /etc/init.d/sendsigs calls
> killall5 binary from sysvinit-utils, killing almost all running
> processes.
>
> Of course it never should kill nbd-client, so the /etc/init.d/nbd-client
> script is smart enough to register its PID to be exempt from sendsig's
> action: by recording it in the /run/sendsigs.omit.d/nbd-cient file.
>
> These PIDs are then collected by /etc/init.d/sendsig and passed as "-o
> NNN" options to killall5 which spares those processes from premature
> termination.
>
> However, before killall5 goes on to kill all the other processes, it
> does a:
>

>     /* Now stop all processes. */
>     kill(-1, SIGSTOP);

>
> And when it's done, it does:
>

>     /* And let them continue. */
>     kill(-1, SIGCONT);

>
> These SIGSTOP, SIGCONT signals are passed to all processes, including
> nbd-client. Unfortunately nbd-client is written in a way that makes it
> unable to handle any signals delivered while it is inside an ioctl call,
> and it looses its server connection on SIGSTOP, totally breaking the
> block devices it provides.
>
> What would be the right way to prevent this problem? Fix sysvinit?

My inclination here is that killall5 shouldn't send any signals (including a
STOP CONT pair) to processes that have registered to be omitted.

Copying Jesse Smith the sysvinit maintainer.

Jesse what do you think? Is it possible to avoid that?

Thanks

Mark