[systemd-devel] multiple cgroup hierarchies

Łukasz Stelmach l.stelmach at samsung.com
Mon May 12 02:43:33 PDT 2014


I've tried to update systemd to version 212 in Tizen. After I resolved
usual building problems and managed to make my device boot, I hit a
number of "Failed to create cgroup ..." messages. It took me some time
to find the reason (ah, the loveliness of parallel processing) which
appears to be a piece of software that tries to set up its own cgroup
hierarchy and destroys what systemd has done (definitely a
bug). However, I can see a problem with systemd too.

At some point before v212 Lennart decided[1] to lock /sys/fs/cgroup tmpfs
instance mounting it read-only to prevent some issues with shmem.
However this commit also prevents other processes from creating their
own cgroup hierarchies. My question is: is it deliberate? Is there
(going to be?) a way to for "third-party" software to have their own
cgroup hierarchies next to systemd in /sys/fs/cgroup despite of it being
remounted read-only?

[1] http://cgit.freedesktop.org/systemd/systemd/commit/?id=679142ce4a8def7da43c4d3b2a02bae8c0d21175

Kind regards,
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics
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