From mboxrd@z Thu Jan  1 00:00:00 1970
X-Msuck: nntp://news.gmane.io/gmane.comp.sysutils.supervision.general/2569
Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail
From: sysinit@yandex.com
Newsgroups: gmane.comp.sysutils.supervision.general
Subject: race condition in killall
Date: Sun, 5 May 2019 03:55:51 +0200
Message-ID: <20190505015551.GF2595@panda>
References: <20190317132532.GA22622@CasperVector>
 <20190317153002.52c28cf7@dickeberta>
 <20190319124239.GA26884@CasperVector>
 <20190319165853.6bb9f44a@flunder>
 <20190320051439.GA7636@CasperVector>
 <20190504060704.GA27290@CasperVector>
Reply-To: sysinit@yandex.com
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226";
	logging-data="65917"; mail-complaints-to="usenet@blaine.gmane.org"
User-Agent: Mutt/1.10.0 (2018-05-17)
To: supervision@List.skarnet.org
Original-X-From: supervision-return-2159-gcsg-supervision=m.gmane.org@list.skarnet.org Sun May 05 03:55:57 2019
Return-path: <supervision-return-2159-gcsg-supervision=m.gmane.org@list.skarnet.org>
Envelope-to: gcsg-supervision@m.gmane.org
Original-Received: from alyss.skarnet.org ([95.142.172.232])
	by blaine.gmane.org with smtp (Exim 4.89)
	(envelope-from <supervision-return-2159-gcsg-supervision=m.gmane.org@list.skarnet.org>)
	id 1hN6Nh-000H0v-HD
	for gcsg-supervision@m.gmane.org; Sun, 05 May 2019 03:55:57 +0200
Original-Received: (qmail 8123 invoked by uid 89); 5 May 2019 01:56:23 -0000
Mailing-List: contact supervision-help@list.skarnet.org; run by ezmlm
Original-Sender: <supervision@list.skarnet.org>
Precedence: bulk
List-Post: <mailto:supervision@list.skarnet.org>
List-Help: <mailto:supervision-help@list.skarnet.org>
List-Unsubscribe: <mailto:supervision-unsubscribe@list.skarnet.org>
List-Subscribe: <mailto:supervision-subscribe@list.skarnet.org>
List-Id: <supervision.list.skarnet.org>
Original-Received: (qmail 8116 invoked from network); 5 May 2019 01:56:22 -0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex.com; s=mail; t=1557021354;
	bh=wIG07tH9cyIUNGAq2k5ZB0LLUzkuGNFlqlUw8jlD6jA=;
	h=In-Reply-To:Reply-To:Subject:To:From:References:Date:Message-ID;
	b=BL6zPhVCd7Q91ppw1gWbYIET2UKQue9vZJAr9uALzibykJAV276mF6EukRocO+J3B
	 DkjEpowLNLIa2SN7yncb9RxmbRA1deuOAr9EAz5rlJ4pcIcCaESov3caa83j7ePT8a
	 ZF0+h/WWKlnlS6Y6onCcqxFa2ESVCJVa86cNmmKo=
Authentication-Results: mxback7g.mail.yandex.net; dkim=pass header.i=@yandex.com
Content-Disposition: inline
In-Reply-To: <20190504060704.GA27290@CasperVector>
Xref: news.gmane.org gmane.comp.sysutils.supervision.general:2569
Archived-At: <http://permalink.gmane.org/gmane.comp.sysutils.supervision.general/2569>


> pkill(1), killall(1) and killall5(8) all retrieve a process list and
> kill them one by one, instead of calling kill(-1, signal), so a race
> condition can happen thats let some process escape the final SIGKILL.

interesting. i have not considered this at all.
looks like kill( -1, sig ) from process #1 ensures correctnes here
in a cheap and simple way.
so splitting stage 3 into 2 parts seems to be a good approach.

> Since pkill(1) and killall(1) use regex matching, the probability for
> the race can be significantly larger.

since they do more work to select processes and hence need more time when
iterating the PID dirs in the procfs ?
though i doubt they use any matching at all when tasked with killing all
processes and probably behave like the killall5 utility in this situation.

OpenRC also provides a tool for that task btw:
/libexec/rc/bin/kill_all

it uses the kvm method to find running processes on the BSDs and the procfs
on Linux.