** Changed in: ubuntu-power-systems
Importance: Undecided => Medium
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https://bugs.launchpad.net/bugs/1629226
Title:
Bash exits after a few failed fork()-s
Status in The Ubuntu-power-systems project:
New
Status in bash package in Ubuntu:
Invalid
Bug description:
Problem Description
===========================
I write a simple systemd service which will fork child processes fiercely.
But quickly the service failed:
% sudo systemctl status reproducer.service
? reproducer.service - Reproducer of systemd services killed by ips
Loaded: loaded (/etc/systemd/system/reproducer.service; disabled; vendor
preset: enabled)
Active: failed (Result: exit-code) since Fri 2016-03-18 06:58:37 CDT; 2min
43s ago
Process: 5103 ExecStart=/home/hpt/reproducer/reproducer.sh (code=exited,
status=0/SUCCESS)
Main PID: 5105 (code=exited, status=254)
Mar 18 06:58:36 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:36 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 systemd[1]: reproducer.service: Main process exited,
code=exited, status=254/n/a
Mar 18 06:58:37 pinelp3 reproducer.sh[5103]:
/home/hpt/reproducer/reproducer.sh: fork: Resource temporarily unavailable
Mar 18 06:58:37 pinelp3 systemd[1]: reproducer.service: Unit entered failed
state.
Mar 18 06:58:37 pinelp3 systemd[1]: reproducer.service: Failed with result
'exit-code'.
The default task limit of systemd services is 512. Looks like the
service is terminated by the kernel's ips cgroup controller. I think
this isn't correct. Child processes cannot be forked shouldn't cause
parent to die.
% cat /etc/systemd/system/reproducer.service
[Unit]
Description=Reproducer of systemd services killed by ips
After=multi-user.target
[Service]
ExecStart=/home/hpt/reproducer/reproducer.sh
Type=forking
[Install]
WantedBy=multi-user.target
% cat /home/hpt/reproducer/reproducer.sh
#!/bin/bash
foo()
{
#exec sh -c "echo $1: \$\$;sleep 60"
echo $1:
sleep 60
}
bar()
{
c=1
while true
do
for ((i=1;i<=2048;i++))
do
foo $c &
((c++))
done
wait
c=1
done
}
# main
bar &
disown -a
exit 0
---uname output---
Linux pinelp3 4.4.0-12-generic #28-Ubuntu SMP Wed Mar 9 00:40:38 UTC 2016
ppc64le ppc64le ppc64le GNU/Linux
Machine Type = IBM,8408-E8E,lpar
Steps to Reproduce
================================
1. install the simple service in "Problem description"
2. sudo systemctl start reproducer.service
3. wait 2~3 minutes
== Comment: #3 - Vaishnavi Bhat <vaish...@in.ibm.com> - 2016-03-22 11:21:55 ==
From the machine,
root@pinelp3:~# ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 48192
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 48192
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
root@pinelp3:~# ps aux | wc -l --------->While the service is
running
1084
root@pinelp3:~# ps aux | wc -l "
1084
root@pinelp3:~# ps aux | wc -l "
1084
root@pinelp3:~# ps aux | wc -l "
1084
root@pinelp3:~# ps aux | wc -l ---------->While the service is not
running.
572
root@pinelp3:~# free -m --------------> While service is running
total used free shared buff/cache
available
Mem: 12117 628 459 22 11029
9541
Swap: 2052 8 2044
root@pinelp3:~# free -m ------------> while the service is not running.
total used free shared buff/cache
available
Mem: 12117 308 809 22 10999
9890
Swap: 2052 8 2044
== Comment: #4 - Breno Henrique Leitao <bren...@br.ibm.com> - 2016-03-22
11:48:57 ==
This is a new feature in Ubuntu and Systemd that limits the amount of
processes/child created.
You can disable it as doucmented in
https://wiki.ubuntu.com/ppc64el/Recommendations#Max_pids_on_Ubuntu_16.04
== Comment: #5 - Ping Tian Han <pt...@cn.ibm.com> - 2016-03-22 20:24:33 ==
(In reply to comment #4)
> This is a new feature in Ubuntu and Systemd that limits the amount of
> processes/child created.
>
> You can disable it as doucmented in
> https://wiki.ubuntu.com/ppc64el/Recommendations#Max_pids_on_Ubuntu_16.04
Hi,
We knew this feature. But it is then main process of the service
failed when it cannont fork chlid processes. This the problem we want
to know how to fix. Thanks.
== Comment: #6 - Breno Henrique Leitao <bren...@br.ibm.com> - 2016-03-24
13:58:08 ==
Hi,
> We knew this feature. But it is then main process of the service failed when
> it cannont fork chlid processes. This the problem we want to know how to
> fix. Thanks.
What do you want to fix exactly? There was an RFC limiting all systemd
services to spawn, a maximum of process.
This came from the Systemd creator at
https://lists.freedesktop.org/archives/systemd-
devel/2015-November/035006.html.
If you wish to have a service that needs more than 512 process, just
enable it on the service file, as:
[Unit]
Description=Reproducer of systemd services killed by ips
After=multi-user.target
[Service]
ExecStart=/home/hpt/reproducer/reproducer.sh
Type=forking
TasksMax=1024 (or bigger)
[Install]
WantedBy=multi-user.target
Anyway, what are you trying to test exactly, and why do you think it
fails?
== Comment: #7 - Ping Tian Han <pt...@cn.ibm.com> - 2016-03-24 21:26:35 ==
(In reply to comment #6)
> Hi,
>
> > We knew this feature. But it is then main process of the service failed
when
> > it cannont fork chlid processes. This the problem we want to know how to
> > fix. Thanks.
>
> What do you want to fix exactly? There was an RFC limiting all systemd
> services to spawn, a maximum of process.
>
> This came from the Systemd creator at
> https://lists.freedesktop.org/archives/systemd-devel/2015-November/035006.
> html.
>
> If you wish to have a service that needs more than 512 process, just enable
> it on the service file, as:
>
> [Unit]
> Description=Reproducer of systemd services killed by ips
> After=multi-user.target
>
> [Service]
> ExecStart=/home/hpt/reproducer/reproducer.sh
> Type=forking
> TasksMax=1024 (or bigger)
>
> [Install]
> WantedBy=multi-user.target
>
> Anyway, what are you trying to test exactly, and why do you think it fails?
Hi,
We saw that the main process of the example service quited (or
killed?) by some reason when it cannot fork more chlid processes. This
is the problem. We can tolerate that there is only 512 child processes
but cannot if the main process being killed.
We think that even though the main process cannot fork more than 512
child processes, it shouldn't be killed.
thanks.
== Comment: #8 - Breno Henrique Leitao <bren...@br.ibm.com> - 2016-03-29
10:16:04 ==
Hi PIng,
> We think that even though the main process cannot fork more than 512 child
> processes, it shouldn't be killed.
Right. Now I understand your point. So, what is the main process here?
Is it your serivce process, or the systemd process?
PS: I am decreasing the priority to normal, since this is a very
corner case usage.
== Comment: #9 - Kevin W. Rudd <ru...@us.ibm.com> - 2016-03-29 15:50:15 ==
The process in question wasn't killed. It did its own exit:
...
19236 clone(child_stack=0,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x3fff96c25aa0) = -1 EAGAIN (Resource temporarily unavailable)
19236 write(2, "/usr/local/bin/real_forkit.sh: f"..., 70) = 70
19236 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
19236 rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
19236 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
19236 exit_group(254) = ?
19236 +++ exited with 254 +++
The problem here is that the replication script is not *handling* the
error. It is not even looking at the return code of the function it
is trying to fork. It is very possible that the shell itself
triggered its own protection mechanism when faced with a script that
appeared to be running away (the above exit was not after the first
clone failure, but after several calls to clone had failed).
Personally, if I were the admin of this system, this is exactly what I
would want to happen to a run away process (smack it down quickly).
== Comment: #10 - Ping Tian Han <pt...@cn.ibm.com> - 2016-03-29 21:17:16 ==
(In reply to comment #9)
> The process in question wasn't killed. It did its own exit:
>
> ...
> 19236 clone(child_stack=0,
> flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
> child_tidptr=0x3fff96c25aa0) = -1 EAGAIN (Resource temporarily unavailable)
> 19236 write(2, "/usr/local/bin/real_forkit.sh: f"..., 70) = 70
> 19236 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> 19236 rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
> 19236 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> 19236 exit_group(254) = ?
> 19236 +++ exited with 254 +++
>
> The problem here is that the replication script is not *handling* the error.
> It is not even looking at the return code of the function it is trying to
> fork. It is very possible that the shell itself triggered its own
> protection mechanism when faced with a script that appeared to be running
> away (the above exit was not after the first clone failure, but after
> several calls to clone had failed).
>
Thanks, Kevin. Looks like this is a problem of bash? I think there
isn't any reason casuing a shell process as parents to quit just
because it cannot fork more child processes...
> Personally, if I were the admin of this system, this is exactly what I would
> want to happen to a run away process (smack it down quickly).
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