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From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN>
To: 67132-done <at> debbugs.gnu.org
Subject: Re: bug#67132: [Shepherd] Bogus value from PID file can prevent
service from being stopped
In-Reply-To: <87msvizwzh.fsf@HIDDEN> ("Ludovic =?utf-8?Q?Court=C3=A8s=22?=
=?utf-8?Q?'s?= message of "Sun, 12 Nov 2023 18:45:38 +0100")
References: <87msvizwzh.fsf@HIDDEN>
Date: Wed, 22 Nov 2023 11:16:37 +0100
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Ludovic Court=C3=A8s <ludo@HIDDEN> skribis:
> =E2=80=98terminate-process=E2=80=99 in (shepherd service) assumes that, o=
nce it has sent
> SIGKILL to a given PID, it eventually gets a SIGCHLD notification for
> that PID.
>
> Unfortunately there are corner cases where it doesn=E2=80=99t hold. Take=
PID 2:
>
> $ ps x 2
> PID TTY STAT TIME COMMAND
> 2 ? S 0:00 [kthreadd]
>
> That=E2=80=99s not a =E2=80=9Creal=E2=80=9D process, so when you (kill 2 =
SIGKILL), nothing
> happens. Thus, =E2=80=98terminate-process=E2=80=99 never returns; the co=
rresponding
> service stays in =E2=80=9Cstopping=E2=80=9D state and you cannot halt you=
r machine.
Fixed in Shepherd commit cc9c5c029534458ae547d78200b6b51f729654e3.
Ludo=E2=80=99.
Ludovic Courtès <ludo@HIDDEN>:Ludovic Courtès <ludo@HIDDEN>:
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From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN>
To: bug-guix@HIDDEN
Subject: [Shepherd] Bogus value from PID file can prevent service from being
stopped
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Date: Sun, 12 Nov 2023 18:45:38 +0100
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Hi,
=E2=80=98terminate-process=E2=80=99 in (shepherd service) assumes that, onc=
e it has sent
SIGKILL to a given PID, it eventually gets a SIGCHLD notification for
that PID.
Unfortunately there are corner cases where it doesn=E2=80=99t hold. Take P=
ID 2:
--8<---------------cut here---------------start------------->8---
$ ps x 2
PID TTY STAT TIME COMMAND
2 ? S 0:00 [kthreadd]
--8<---------------cut here---------------end--------------->8---
That=E2=80=99s not a =E2=80=9Creal=E2=80=9D process, so when you (kill 2 SI=
GKILL), nothing
happens. Thus, =E2=80=98terminate-process=E2=80=99 never returns; the corr=
esponding
service stays in =E2=80=9Cstopping=E2=80=9D state and you cannot halt your =
machine.
You may wonder how we end up calling =E2=80=98terminate-process=E2=80=99 wi=
th a =E2=80=9Cbogus=E2=80=9D
PID. It normally never happens, but it can happen with a combination of
=E2=80=98make-forkexec-constructor=E2=80=99 with #:pid-file and
=E2=80=98least-authority-wrapper=E2=80=99: the PID file of the wrapper may =
read =E2=80=9C2=E2=80=9D (the
PID inside the least-authority PID namespace), so =E2=80=98herd stop=E2=80=
=99 on that
service will end up doing (kill 2 SIGKILL).
Ludo=E2=80=99.
Ludovic Courtès <ludo@HIDDEN>:bug-guix@HIDDEN.
Full text available.bug-guix@HIDDEN:bug#67132; Package guix.
Full text available.
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