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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1b7b567..5a2fcf5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1362,8 +1362,11 @@
removed_mask = root->subsys_mask & ~opts.subsys_mask;
/* Don't allow flags or name to change at remount */
- if (opts.flags != root->flags ||
+ if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
(opts.name && strcmp(opts.name, root->name))) {
+ pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n",
+ opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
+ root->flags & CGRP_ROOT_OPTION_MASK, root->name);
ret = -EINVAL;
goto out_unlock;
}