Patch "cgroup: fix rule checking for threaded mode switching" has been added to the 4.14-stable tree

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

cgroup: fix rule checking for threaded mode switching

to the 4.14-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-fix-rule-checking-for-threaded-mode-switching.patch
and it can be found in the queue-4.14 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: Wed, 21 Feb 2018 11:39:22 -0800
Subject: cgroup: fix rule checking for threaded mode switching

From: Tejun Heo <[email protected]>

commit d1897c9538edafd4ae6bbd03cc075962ddde2c21 upstream.

A domain cgroup isn't allowed to be turned threaded if its subtree is populated or domain controllers are enabled. cgroup_enable_threaded() depended on cgroup_can_be_thread_root() test to enforce this rule. A parent which has populated domain descendants or have domain controllers enabled can't become a thread root, so the above rules are enforced automatically.

However, for the root cgroup which can host mixed domain and threaded children, cgroup_can_be_thread_root() doesn't check any of those conditions and thus first level cgroups ends up escaping those rules.

This patch fixes the bug by adding explicit checks for those rules in cgroup_enable_threaded().

---
 kernel/cgroup/cgroup.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -3148,6 +3148,16 @@ static int cgroup_enable_threaded(struct
 	if (cgroup_is_threaded(cgrp))
 		return 0;
 
+	/*
+	 * If @cgroup is populated or has domain controllers enabled, it
+	 * can't be switched.  While the below cgroup_can_be_thread_root()
+	 * test can catch the same conditions, that's only when @parent is
+	 * not mixable, so let's check it explicitly.
+	 */
+	if (cgroup_is_populated(cgrp) ||
+	    cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask)
+		return -EOPNOTSUPP;
+
 	/* we're joining the parent's domain, ensure its validity */
 	if (!cgroup_is_valid_domain(dom_cgrp) ||
 	    !cgroup_can_be_thread_root(dom_cgrp))

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

queue-4.14/libata-disable-lpm-for-crucial-bx100-ssd-500gb-drive.patch queue-4.14/libata-apply-nolpm-quirk-to-crucial-m500-480-and-960gb-ssds.patch queue-4.14/libata-fix-length-validation-of-atapi-relayed-scsi-commands.patch queue-4.14/libata-apply-nolpm-quirk-to-crucial-mx100-512gb-ssds.patch queue-4.14/pci-add-function-1-dma-alias-quirk-for-highpoint-rocketraid-644l.patch queue-4.14/libata-modify-quirks-for-mx100-to-limit-ncq_trim-quirk-to-mu01-version.patch queue-4.14/libata-enable-queued-trim-for-samsung-ssd-860.patch queue-4.14/ahci-add-pci-id-for-the-highpoint-rocketraid-644l-card.patch queue-4.14/cgroup-fix-rule-checking-for-threaded-mode-switching.patch queue-4.14/libata-make-crucial-bx100-500gb-lpm-quirk-apply-to-all-firmware-versions.patch queue-4.14/libata-remove-warn-for-dma-or-pio-command-without-data.patch queue-4.14/libata-don-t-try-to-pass-through-ncq-commands-to-non-ncq-devices.patch