linux-next: cgroup_mount() falls asleep forever

[Andrey Wagin]

Hi All,

I execute CRIU tests on linux-next. Today I found that one of tests
hangs up forever.

[root@linux-next-test linux-next]# git describe HEAD
next-20140922
[root@linux-next-test ~]# ps axf
...
  698 ?        Ss     0:05  \_ sshd: root@notty
  700 ?        Ss     0:00  |   \_ bash -x
jenkins-scripts/jenkins-ct.sh jenkins.sh
  706 ?        S      0:00  |       \_ bash -c ( mount --make-rprivate
/ && umount -l  /proc && mount -t proc proc /proc/ && bash -x
jenkins.sh)
  707 ?        S      0:00  |           \_ bash -c ( mount
--make-rprivate / && umount -l  /proc && mount -t proc proc /proc/ &&
bash -x jenkins.sh)
  711 ?        S      0:00  |               \_ bash -x jenkins.sh
 2981 ?        S      0:05  |                   \_ bash -x
test/zdtm.sh -C -x .*\(maps01\|maps04\)
 6717 ?        S      0:00  |                       \_ /bin/bash
zdtm/live/static/cgroup00.hook --clean
 6719 ?        D     11:13  |                           \_ mount -t
cgroup none cgclean.cWgK71 -o none,name=zdtmtst

[root@linux-next-test ~]# cat /proc/6719/stack
[<ffffffff8111fcb7>] msleep+0x37/0x50
[<ffffffff8114bde2>] cgroup_mount+0x712/0xa50
[<ffffffff8124d0e9>] mount_fs+0x39/0x1b0
[<ffffffff8126d76b>] vfs_kern_mount+0x6b/0x150
[<ffffffff8127075b>] do_mount+0x22b/0xc20
[<ffffffff81271492>] SyS_mount+0xa2/0x110
[<ffffffff817e3ba9>] system_call_fastpath+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff

Let me know which info do you need for investigation.

Steps to reproduce:

git clone https://github.com/xemul/criu.git
cd criu
make
bash test/zdtm.sh static/cgroup00

Thanks,
Andrew
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