Commits
Tejun Heo committed 0ce6cba3577
cgroup: CGRP_ROOT_SUBSYS_BOUND should be ignored when comparing mount options
1672d04070 ("cgroup: fix cgroupfs_root early destruction path")
introduced CGRP_ROOT_SUBSYS_BOUND which is used to mark completion of
subsys binding on a new root; however, this broke remounts.
cgroup_remount() doesn't allow changing root options via remount and
CGRP_ROOT_SUBSYS_BOUND, which is set on all fully initialized roots,
makes the function reject all remounts.
Fix it by putting the options part in the lower 16 bits of root->flags
and masking the comparions. While at it, make cgroup_remount() emit
an error message explaining why it's rejecting a remount request, so
that it's less of a mystery.
Signed-off-by: Tejun Heo <tj@kernel.org>