Re: memcg creates an unkillable task in 3.2-rc2

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

> I am also seeing what looks like a leak somewhere in the cgroup code as
> well.  After some runs of the same reproducer I get into a state where
> after everything is clean up.  All of the control groups have been
> removed and the cgroup filesystem is unmounted, I can mount a cgroup
> filesystem with that same combindation of subsystems, but I can't mount
> a cgroup filesystem with any of those subsystems in any other
> combination.  So I am guessing that the superblock is from the original
> mounting is still lingering for some reason.
> 

If this happens again, you can check /proc/cgroups, 

#subsys_name    hierarchy       num_cgroups     enabled
cpuset  0       1       1
debug   0       1       1
cpu     0       1       1
cpuacct 0       1       1
memory  0       1       1
devices 0       1       1
freezer 0       1       1
blkio   0       1       1

If "hierachy" is not 0, then it didn't really unmounted. If "num_cgroups"
is not 1, then there're some cgroups not really destroyed though they've
been rmdired.