Message-ID: <5967400.cFS0L5jxeH@merkaba>
Date:   Mon, 19 Dec 2016 13:06:00 +0100
From:   Martin Steigerwald <martin.steigerwald@...mix.de>
To:     Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...l.org>
CC:     Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Balbir Singh <balbir@...ibm.com>,
        Shailabh Nagar <nagar@...son.ibm.com>,
        Jay Lan <jlan@...r.sgi.com>,
        Martin Steigerwald <martin@...htvoll.de>,
        Gerlof Langeveld <gerlof.langeveld@...ptool.nl>,
        Marc Haber <mh+debian-packages@...schlus.de>,
        Martin <martin@...htvoll.de>
Subject: [REGRESSION] Two issues that prevent process accounting (taskstats) from working correctly

Hello Ingo, Peter, Nicolas, Andrew, Balbir, Shailabh, Jay, Gerlof and Marc,

starting from a Debian bug report of mine, Gerlof Langeveld, developer of 
system and process monitor atop¹, found two issues with process accounting.

[1] http://atoptool.nl/


I did some guess work on who might be the maintainer for this, but please feel 
free to add further Cc´s as you see fit. Or ask for removal for Cc if you are 
not working on this anymore.

Gerlof found two issues which I also reported to the kernel bug tracker. I 
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, 
which means that process accounting is activated successfully.
However, no process accounting records are written whatsoever. This 
situation can be reproduced with the program 'acctdemo.c'
that you can find as attachment. When this program gives the message 
"found a process accounting record!", the situation is okay
and process accounting works fine to the file '/tmp/mypacct'. When the 
message 'No process accounting record yet....' is repeatedly given,
process accounting does not work and will not work at all. It might be 
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 
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 
with a 4.8 kernel.

I reported this as:

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



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

The code that is used by the atopacctd daemon is based on the demo code 
'getdelays.c' that can be found in the kernel source code tree
(..../linux/Documentation/accounting/getdelays.c). Also this 'getdelays' 
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 
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 
an incompatibility introduced by the kernel code.
It would be nice if the kernel maintainers provide a working version of 
the getdelays program in the kernel source tree.

I only experience this problem on Debian8 with a 4.8 kernel (virtual 
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 
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 
TASKSTATS_CMD_GET returns -EINVAL

https://bugzilla.kernel.org/show_bug.cgi?id=190711


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

Thanks,
-- 
Martin Steigerwald  | Trainer

teamix GmbH
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