s6-rc transition failures

From: Van Bemten, Lionel (Nokia - BE/Antwerp) <"Van>
Date: Thu, 15 Jun 2017 16:30:06 +0000

Hello all,

I am facing questions regarding the way to correctly handle
transition failures with s6-rc. The new permanent failure feature
already clarifies some scenarios but I still have doubts about
some cases. Below are two concrete examples. I would
be happy to have remarks or suggestions about how to cope
with them clean and nice :).

1. I start a longrun service with "s6-rc -u change svc". This
service hangs and never reaches readiness notification. After
timeout s6-rc will declare the transition a failure. But the process
is actually running and I have no way to stop it through s6-rc.
The only way is to issue "s6-svc -d /path/to/svc". But then I have
the feeling I am doing something in the back of s6-rc to unblock
the situation because s6-rc cannot handle it. Somehow I wish
s6-rc had an extra state BUSY between DOWN and UP when
the transition is ongoing, and that it could bring me back to
DOWN when I ask it to.

2. Slightly related, I have an issue with system shutdown. I am
working on a buildroot system and specifically I use the
/etc/rc.tini which can be found here [1] and which is executed
as part of the shutdown sequence of the system. The problem
is with the invocation of "s6-rc -b -da change" (I added the -b).
If there is already an s6-rc ongoing, the shutdown sequence will
be blocked until the first s6-rc times out. And this kind of timeout
is of the order of minutes as I have slow services depending
on each other. I currently think the best thing to do is to is to
"killall s6-rc" before calling "s6-rc -ad change". This leaves a little
race condition possible, but more importantly, I have concerns
about killing an ongoing s6-rc. This will leave longrun services
in the middle of a state transition - there is the connection with
the first scenario - and I expect the final effect is that the
finish script will not be executed before the system goes down,
which is precisely what I want to happen when I call
"s6-rc -ad change". Secondly, I do not know what effect this will
have on oneshots. I fear "/etc/init.d/S98xxx start" will still be
running and "/etc/init.d/S98xxx stop" will be executed - the thought
of which horrifies me beyond reasoning.

[1] https://github.com/elebihan/s6-br2-init-skeleton/blob/master/data/skeleton/etc/rc.tini

Thanks in advance for any idea that might help me :).

Received on Thu Jun 15 2017 - 16:30:06 UTC

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