Hello, We run CRIU tests on linux-next kernels. Today, I found that our test robot hangs up on mounting a cgroup file system. https://travis-ci.org/avagin/linux/jobs/455732006 632 ? Ssl 0:00 /usr/bin/containerd 843 ? Sl 0:00 \_ containerd-shim -namespace moby -workdir /var/lib/containerd/io.containerd.runtime.v1.linux/moby/c2311352d53eed1f5094580102e41c2a02eaf98b8626c86ccf314599101b26 862 pts/0 Ss+ 0:00 \_ python test/zdtm.py run -T zdtm/static/cgroup.* 1652 pts/0 S+ 0:00 \_ flock zdtm_mount_cgroups.lock ./zdtm_umount_cgroups 1653 pts/0 S+ 0:00 \_ /bin/sh ./zdtm_umount_cgroups 1659 pts/0 D+ 0:06 \_ mount -t cgroup -o none,name=zdtmtst.defaultroot zdtm zdtm.9QFGko [root@fc24 ~]# cat /proc/1659/stack [<0>] msleep+0x38/0x40 [<0>] cgroup1_get_tree+0x4e1/0x749 [<0>] vfs_get_tree+0x5e/0x140 [<0>] do_mount+0x326/0xc70 [<0>] ksys_mount+0xba/0xd0 [<0>] __x64_sys_mount+0x21/0x30 [<0>] do_syscall_64+0x60/0x210 [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe [<0>] 0xffffffffffffffff [root@fc24 ~]# cat /proc/1659/cgroup | grep zdtm 13:name=zdtmtst.defaultroot:/ 12:name=zdtmtst:/ [root@fc24 ~]# strace -fp 1659 strace: Process 1659 attached mount("zdtm", "/criu/test/zdtm.9QFGko", "cgroup", MS_MGC_VAL, "none,name=zdtmtst.defaultroot") = ? ERESTARTNOINTR (To be restarted) mount("zdtm", "/criu/test/zdtm.9QFGko", "cgroup", MS_MGC_VAL, "none,name=zdtmtst.defaultroot") = ? ERESTARTNOINTR (To be restarted) mount("zdtm", "/criu/test/zdtm.9QFGko", "cgroup", MS_MGC_VAL, "none,name=zdtmtst.defaultroot") = ? ERESTARTNOINTR (To be restarted) mount("zdtm", "/criu/test/zdtm.9QFGko", "cgroup", MS_MGC_VAL, "none,name=zdtmtst.defaultroot") = ? ERESTARTNOINTR (To be restarted) mount("zdtm", "/criu/test/zdtm.9QFGko", "cgroup", MS_MGC_VAL, "none,name=zdtmtst.defaultroot") = ? ERESTARTNOINTR (To be restarted) Steps to reproduce: I don't know how to reproduce this issue without running criu tests. I tried to create a simple reproducer, but I failed. So I created a docker container and the problem can be reproduced by running this command: docker run --rm -it --privileged -v /lib/modules:/lib/modules --tmpfs /run docker.io/avagin/criu-fc29-cgroup python test/zdtm.py run -T 'zdtm/static/cgroup.*' I found that something wrong is in [16ec1a5d58ea67ba737d3a66efe9e53c6bb149f7] kernfs, sysfs, cgroup, intel_rdt: Support fs_context https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20181116&id=16ec1a5d58ea67ba737d3a66efe9e53c6bb149f7 Thanks, Andrei