cgroup: deprecate remount option changes

This patch marks the following features for deprecation.

* Rebinding subsys by remount: Never reached useful state - only works
  on empty hierarchies.

* release_agent update by remount: release_agent itself will be
  replaced with conventional fsnotify notification.

v2: Lennart pointed out that "name=" is necessary for mounts w/o any
    controller attached.  Drop "name=" deprecation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>

2 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index c1be8066ea59..5298e126cea3 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -539,3 +539,12 @@ Why:	There appear to be no production users of the get_robust_list syscall,
         of ASLR. It was only ever intended for debugging, so it should be
         removed.
 Who:    Kees Cook <keescook@chromium.org>
+
+----------------------------
+
+What:   cgroup option updates via remount
+When:   March 2013
+Why:    Remount currently allows changing bound subsystems and
+        release_agent.  Rebinding is hardly useful as it only works
+        when the hierarchy is empty and release_agent itself should be
+        replaced with conventional fsnotify.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ed64ccac67c9..741c120e06c1 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1294,6 +1294,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
         if (ret)
                 goto out_unlock;
 
+        /* See feature-removal-schedule.txt */
+        if (opts.subsys_bits != root->actual_subsys_bits || opts.release_agent)
+                pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
+                           task_tgid_nr(current), current->comm);
+
         /* Don't allow flags or name to change at remount */
         if (opts.flags != root->flags ||
             (opts.name && strcmp(opts.name, root->name))) {