Patch "cgroup: create dfl_root files on subsys registration" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

cgroup: create dfl_root files on subsys registration

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cgroup-create-dfl_root-files-on-subsys-registration.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Tejun Heo <[email protected]>
Date: Tue, 18 Jul 2017 17:57:46 -0400
Subject: cgroup: create dfl_root files on subsys registration

From: Tejun Heo <[email protected]>

commit 7af608e4f9530372aec6e940552bf76595f2e265 upstream.

On subsystem registration, css_populate_dir() is not called on the new root css, so the interface files for the subsystem on cgrp_dfl_root aren't created on registration. This is a residue from the days when cgrp_dfl_root was used only as the parking spot for unused subsystems, which no longer is true as it's used as the root for cgroup2.

This is often fine as later operations tend to create them as a part of mount (cgroup1) or subtree_control operations (cgroup2); however, it's not difficult to mount cgroup2 with the controller interface files missing as Waiman found out.

Fix it by invoking css_populate_dir() on the root css on subsys registration.

---
 kernel/cgroup/cgroup.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -4578,6 +4578,10 @@ int __init cgroup_init(void)
 
 		if (ss->bind)
 			ss->bind(init_css_set.subsys[ssid]);
+
+		mutex_lock(&cgroup_mutex);
+		css_populate_dir(init_css_set.subsys[ssid]);
+		mutex_unlock(&cgroup_mutex);
 	}
 
 	/* init_css_set.subsys[] has been updated, re-hash */

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/cgroup-don-t-call-migration-methods-if-there-are-no-tasks-to-migrate.patch queue-4.12/cgroup-create-dfl_root-files-on-subsys-registration.patch queue-4.12/cgroup-fix-error-return-value-from-cgroup_subtree_control.patch queue-4.12/workqueue-restore-wq_unbound-max_active-1-to-be-ordered.patch queue-4.12/libata-array-underflow-in-ata_find_dev.patch