From: Martin Steigerwald <martin.steigerwald@teamix.de>
To: Ingo Molnar <mingo@kernel.org>, Andrew Morton <akpm@osdl.org>
CC: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Balbir Singh <balbir@in.ibm.com>,
        Shailabh Nagar <nagar@watson.ibm.com>, Jay Lan <jlan@engr.sgi.com>,
        Martin Steigerwald <martin@lichtvoll.de>,
        Gerlof Langeveld <gerlof.langeveld@atoptool.nl>,
        Marc Haber <mh+debian-packages@zugschlus.de>,
        Martin <martin@lichtvoll.de>
Subject: [REGRESSION] Two issues that prevent process accounting (taskstats) from working correctly
Date: Mon, 19 Dec 2016 13:06:00 +0100
Message-ID: <5967400.cFS0L5jxeH@merkaba>
Organization: teamix GmbH
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=EF=BB=BFHello Ingo, Peter, Nicolas, Andrew, Balbir, Shailabh, Jay, Gerlof =
and Marc,

starting from a Debian bug report of mine, Gerlof Langeveld, developer of=20
system and process monitor atop=C2=B9, found two issues with process accoun=
ting.

[1] http://atoptool.nl/


I did some guess work on who might be the maintainer for this, but please f=
eel=20
free to add further Cc=C2=B4s as you see fit. Or ask for removal for Cc if =
you are=20
not working on this anymore.

Gerlof found two issues which I also reported to the kernel bug tracker. I=
=20
copy and paste the summaries that Gerlof prepared:


1) Sometimes process accounting does not work at all.

The acct() system call (to activate process accounting) return value 0,=20
which means that process accounting is activated successfully.
However, no process accounting records are written whatsoever. This=20
situation can be reproduced with the program 'acctdemo.c'
that you can find as attachment. When this program gives the message=20
"found a process accounting record!", the situation is okay
and process accounting works fine to the file '/tmp/mypacct'. When the=20
message 'No process accounting record yet....' is repeatedly given,
process accounting does not work and will not work at all. It might be=20
that you have to start this program several times before you get
this situation (preferably start/finish lots of processes in the mean time)=
.
This problem is probably caused by a new mechanism introduced in the=20
kernel code (..../linux/kernel/acct.c) that is called 'slow accounting'
and has to be solved in the kernel code.

I experience this problem on Debian8 with a 4.8 kernel and on CentOS7=20
with a 4.8 kernel.

I reported this as:

Bug 190271 - process accounting sometimes does not work=20
https://bugzilla.kernel.org/show_bug.cgi?id=3D190271


2) When using the NETLINK inface, the command TASKSTATS_CMD_GET=20
consequently returns -EINVAL.

The code that is used by the atopacctd daemon is based on the demo code=20
'getdelays.c' that can be found in the kernel source code tree
(..../linux/Documentation/accounting/getdelays.c). Also this 'getdelays'=20
program does not work any more (also -EINVAL on the same call)
with the newer kernels. I really spent a lot of time on this issue to=20
get the code running (there are many places in the kernel code where
-EINVAL for this call can be given), but I did not succeed. It is really=20
an incompatibility introduced by the kernel code.
It would be nice if the kernel maintainers provide a working version of=20
the getdelays program in the kernel source tree.

I only experience this problem on Debian8 with a 4.8 kernel (virtual=20
machine with 4 cores).
On CentOS7 with a 4.8 kernel it works fine (physical machine with 4 cores).

I will anyhow adapt atopacctd for this issue that it detects and logs=20
the -EINVAL and terminates.
The current version of atopacctd keeps running which is not useful at all.


I reported this as:

Bug 190711 - Process accounting: Using the NETLINK inface, the command=20
TASKSTATS_CMD_GET returns -EINVAL

https://bugzilla.kernel.org/show_bug.cgi?id=3D190711


Marc Haber, maintainer of atop package, Gerlof Langeveld, developer of atop=
=20
and I are currently discussing workarounds with atop and/or systemd service=
=20
fail for the time till upstream kernels with this issues fixed are shipped =
by=20
distributions. Still it would be nice to remove those work-arounds and have=
=20
the kernel work correctly again at some time in the future.

Thanks,
--=20
Martin Steigerwald  | Trainer

teamix GmbH
S=C3=BCdwestpark 43
90449 N=C3=BCrnberg

Tel.:  +49 911 30999 55 | Fax: +49 911 30999 99
mail: martin.steigerwald@teamix.de | web:  http://www.teamix.de | blog: htt=
p://blog.teamix.de

Amtsgericht N=C3=BCrnberg, HRB 18320 | Gesch=C3=A4ftsf=C3=BChrer: Oliver K=
=C3=BCgow, Richard M=C3=BCller

teamix Support Hotline: +49 911 30999-112
=20
 *** Bitte liken Sie uns auf Facebook: facebook.com/teamix ***


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Content-Disposition: attachment; filename="acctdemo.c"
Content-Transfer-Encoding: 7Bit
Content-Type: text/x-csrc; charset="UTF-8"; name="acctdemo.c"

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#define ACCTFILE	"/tmp/mypacct"

main()
{
	int  fd;
	char buf[1024];

	if ( (fd = open(ACCTFILE, O_RDWR|O_CREAT|O_TRUNC, 0777)) == -1)
	{
		perror("Open " ACCTFILE);
		exit(1);
	}

	if (acct(ACCTFILE) == -1)
	{
		perror("Switch on accounting");
		exit(1);
	}

	if ( fork() == 0 )	// fork new process
		exit(0);	// child process: finish


	// parent process:
	//	wait for child to finish

	wait((int *)0);

	// 	read the process accounting record of the finished child

	while (read(fd, buf, sizeof buf) == 0)
	{
		printf("No process accounting record yet....\n");
		sleep(1);
	}

	printf("Yeeeeah, found a process accounting record!\n");
}

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