Patch "sched, cgroup: Don't reject lower cpu.max on ancestors" has been added to the 4.15-stable tree

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

sched, cgroup: Don't reject lower cpu.max on ancestors

to the 4.15-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:
sched-cgroup-don-t-reject-lower-cpu.max-on-ancestors.patch
and it can be found in the queue-4.15 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: Mon, 22 Jan 2018 11:26:18 -0800
Subject: sched, cgroup: Don't reject lower cpu.max on ancestors

From: Tejun Heo <[email protected]>

commit c53593e5cb693d59d9e8b64fb3a79436bf99c3b3 upstream.

While adding cgroup2 interface for the cpu controller, 0d5936344f30 ("sched: Implement interface for cgroup unified hierarchy") forgot to update input validation and left it to reject cpu.max config if any descendant has set a higher value.

cgroup2 officially supports delegation and a descendant must not be able to restrict what its ancestors can configure. For absolute limits such as cpu.max and memory.max, this means that the config at each level should only act as the upper limit at that level and shouldn't interfere with what other cgroups can configure.

This patch updates config validation on cgroup2 so that the cpu controller follows the same convention.

---
 kernel/sched/core.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

@@ -6611,13 +6611,18 @@ static int tg_cfs_schedulable_down(struc
 		parent_quota = parent_b->hierarchical_quota;
 
 		/*
-		 * Ensure max(child_quota) <= parent_quota, inherit when no
+		 * Ensure max(child_quota) <= parent_quota.  On cgroup2,
+		 * always take the min.  On cgroup1, only inherit when no
 		 * limit is set:
 		 */
-		if (quota == RUNTIME_INF)
-			quota = parent_quota;
-		else if (parent_quota != RUNTIME_INF && quota > parent_quota)
-			return -EINVAL;
+		if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
+			quota = min(quota, parent_quota);
+		} else {
+			if (quota == RUNTIME_INF)
+				quota = parent_quota;
+			else if (parent_quota != RUNTIME_INF && quota > parent_quota)
+				return -EINVAL;
+		}
 	}
 	cfs_b->hierarchical_quota = quota;
 

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

queue-4.15/libata-disable-lpm-for-crucial-bx100-ssd-500gb-drive.patch queue-4.15/libata-apply-nolpm-quirk-to-crucial-m500-480-and-960gb-ssds.patch queue-4.15/sched-cgroup-don-t-reject-lower-cpu.max-on-ancestors.patch queue-4.15/libata-fix-length-validation-of-atapi-relayed-scsi-commands.patch queue-4.15/libata-apply-nolpm-quirk-to-crucial-mx100-512gb-ssds.patch queue-4.15/pci-add-function-1-dma-alias-quirk-for-highpoint-rocketraid-644l.patch queue-4.15/libata-modify-quirks-for-mx100-to-limit-ncq_trim-quirk-to-mu01-version.patch queue-4.15/libata-enable-queued-trim-for-samsung-ssd-860.patch queue-4.15/ahci-add-pci-id-for-the-highpoint-rocketraid-644l-card.patch queue-4.15/cgroup-fix-rule-checking-for-threaded-mode-switching.patch queue-4.15/libata-make-crucial-bx100-500gb-lpm-quirk-apply-to-all-firmware-versions.patch queue-4.15/libata-remove-warn-for-dma-or-pio-command-without-data.patch queue-4.15/libata-don-t-try-to-pass-through-ncq-commands-to-non-ncq-devices.patch