Bug#823530: systemd 228 reduced maximum number of tasks in a cgroup to 512 by default

[Sebastian Schmidt]

Package: systemd
Version: 229-3
Severity: normal
Tags: upstream

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Hi,

Whilst debugging why Chrome would regularly fail to create new
threads[1] and zsh couldn’t fork I noticed that:
- - All affected processes run in the /system.slice/xdm.service cgroup
- - “systemctl status xdm.service” says “Tasks: 476 (limit: 512)”
- - The changelog for systemd 228 reads[2]:

        There's a new system.conf setting DefaultTasksMax= to control
        the default TasksMax= setting for services and scopes running on
        the system.
        […]
        The setting now defaults to 512, which means services that are
        not explicitly configured otherwise will only be able to create
        512 processes or threads at maximum, from this version on.

- - Nothing in xdm’s PAM configuration would load pam_systemd for creating
  a session.

I’m not sure whether using pam_systemd would actually fix that; but
even then I find this new limit per cgroup at least surprising and
it apparently breaks a lot of software.

Sebastian

1: https://crbug.com/602002
2: https://github.com/systemd/systemd/blob/ccddd104fc95e0e769142af6e1fe1edec5be70a6/NEWS#L373-393

- -- Package-specific info:

- -- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.6.0-rc5-amd64 (SMP w/4 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

Versions of packages systemd depends on:
ii  adduser         3.114
ii  libacl1         2.2.52-3
ii  libapparmor1    2.10-3+b1
ii  libaudit1       1:2.4.5-1+b1
ii  libblkid1       2.27.1-6
ii  libc6           2.22-4
ii  libcap2         1:2.24-12
ii  libcap2-bin     1:2.24-12
ii  libcryptsetup4  2:1.7.0-2
ii  libgcrypt20     1.6.5-2
ii  libgpg-error0   1.21-2
ii  libkmod2        22-1
ii  liblzma5        5.1.1alpha+20120614-2.1
ii  libmount1       2.27.1-6
ii  libpam0g        1.1.8-3.2
ii  libseccomp2     2.2.3-3
ii  libselinux1     2.4-3+b1
ii  libsystemd0     229-3
ii  mount           2.27.1-6
ii  util-linux      2.27.1-6

Versions of packages systemd recommends:
ii  dbus            1.10.8-1
ii  libpam-systemd  229-3

Versions of packages systemd suggests:
pn  systemd-container  <none>
pn  systemd-ui         <none>

Versions of packages systemd is related to:
ii  udev  229-3

- -- Configuration Files:
/etc/systemd/logind.conf changed [not included]
/etc/systemd/system.conf changed [not included]

- -- no debconf information

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