Merge branch 'for-5.3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fix from Tejun Heo:
 "Roman found and fixed a bug in the cgroup2 freezer which allows new
  child cgroup to escape frozen state"

* 'for-5.3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: freezer: fix frozen state inheritance
  kselftests: cgroup: add freezer mkdir test

kernel/cgroup/cgroup.c

@@ -5255,8 +5255,16 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	 * if the parent has to be frozen, the child has too.
 	 */
 	cgrp->freezer.e_freeze = parent->freezer.e_freeze;
-	if (cgrp->freezer.e_freeze)
+	if (cgrp->freezer.e_freeze) {
+		/*
+		 * Set the CGRP_FREEZE flag, so when a process will be
+		 * attached to the child cgroup, it will become frozen.
+		 * At this point the new cgroup is unpopulated, so we can
+		 * consider it frozen immediately.
+		 */
+		set_bit(CGRP_FREEZE, &cgrp->flags);
 		set_bit(CGRP_FROZEN, &cgrp->flags);
+	}
 
 	spin_lock_irq(&css_set_lock);
 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {

tools/testing/selftests/cgroup/test_freezer.c

@@ -447,6 +447,59 @@ cleanup:
 	return ret;
 }
 
+/*
+ * The test creates a cgroups and freezes it. Then it creates a child cgroup
+ * and populates it with a task. After that it checks that the child cgroup
+ * is frozen and the parent cgroup remains frozen too.
+ */
+static int test_cgfreezer_mkdir(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *parent, *child = NULL;
+	int pid;
+
+	parent = cg_name(root, "cg_test_mkdir_A");
+	if (!parent)
+		goto cleanup;
+
+	child = cg_name(parent, "cg_test_mkdir_B");
+	if (!child)
+		goto cleanup;
+
+	if (cg_create(parent))
+		goto cleanup;
+
+	if (cg_freeze_wait(parent, true))
+		goto cleanup;
+
+	if (cg_create(child))
+		goto cleanup;
+
+	pid = cg_run_nowait(child, child_fn, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	if (cg_wait_for_proc_count(child, 1))
+		goto cleanup;
+
+	if (cg_check_frozen(child, true))
+		goto cleanup;
+
+	if (cg_check_frozen(parent, true))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (child)
+		cg_destroy(child);
+	free(child);
+	if (parent)
+		cg_destroy(parent);
+	free(parent);
+	return ret;
+}
+
 /*
  * The test creates two nested cgroups, freezes the parent
  * and removes the child. Then it checks that the parent cgroup
@@ -815,6 +868,7 @@ struct cgfreezer_test {
 	T(test_cgfreezer_simple),
 	T(test_cgfreezer_tree),
 	T(test_cgfreezer_forkbomb),
+	T(test_cgfreezer_mkdir),
 	T(test_cgfreezer_rmdir),
 	T(test_cgfreezer_migrate),
 	T(test_cgfreezer_ptrace),