1 files changed, 30 insertions, 19 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 48851327a15e..c3c9a0e1b3c9 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -189,7 +189,7 @@ static u16 have_canfork_callback __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
-	.count		= { .counter = 2, },
+	.count		= REFCOUNT_INIT(2),
 	.user_ns	= &init_user_ns,
 	.ns.ops		= &cgroupns_operations,
 	.ns.inum	= PROC_CGROUP_INIT_INO,
@@ -436,7 +436,12 @@ out_unlock:
 	return css;
 }
 
-static void cgroup_get(struct cgroup *cgrp)
+static void __maybe_unused cgroup_get(struct cgroup *cgrp)
+{
+	css_get(&cgrp->self);
+}
+
+static void cgroup_get_live(struct cgroup *cgrp)
 {
 	WARN_ON_ONCE(cgroup_is_dead(cgrp));
 	css_get(&cgrp->self);
@@ -554,7 +559,7 @@ EXPORT_SYMBOL_GPL(of_css);
  * haven't been created.
  */
 struct css_set init_css_set = {
-	.refcount		= ATOMIC_INIT(1),
+	.refcount		= REFCOUNT_INIT(1),
 	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
 	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
 	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
@@ -724,7 +729,7 @@ void put_css_set_locked(struct css_set *cset)
 
 	lockdep_assert_held(&css_set_lock);
 
-	if (!atomic_dec_and_test(&cset->refcount))
+	if (!refcount_dec_and_test(&cset->refcount))
 		return;
 
 	/* This css_set is dead. unlink it and release cgroup and css refs */
@@ -932,7 +937,7 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
 	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
 
 	if (cgroup_parent(cgrp))
-		cgroup_get(cgrp);
+		cgroup_get_live(cgrp);
 }
 
 /**
@@ -977,7 +982,7 @@ static struct css_set *find_css_set(struct css_set *old_cset,
 		return NULL;
 	}
 
-	atomic_set(&cset->refcount, 1);
+	refcount_set(&cset->refcount, 1);
 	INIT_LIST_HEAD(&cset->tasks);
 	INIT_LIST_HEAD(&cset->mg_tasks);
 	INIT_LIST_HEAD(&cset->task_iters);
@@ -1640,7 +1645,7 @@ void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
 		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
 }
 
-int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
+int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
 {
 	LIST_HEAD(tmp_links);
 	struct cgroup *root_cgrp = &root->cgrp;
@@ -1656,8 +1661,8 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	root_cgrp->id = ret;
 	root_cgrp->ancestor_ids[0] = ret;
 
-	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
-			      GFP_KERNEL);
+	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
+			      ref_flags, GFP_KERNEL);
 	if (ret)
 		goto out;
 
@@ -1802,7 +1807,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 			return ERR_PTR(-EINVAL);
 		}
 		cgrp_dfl_visible = true;
-		cgroup_get(&cgrp_dfl_root.cgrp);
+		cgroup_get_live(&cgrp_dfl_root.cgrp);
 
 		dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
 					 CGROUP2_SUPER_MAGIC, ns);
@@ -2425,11 +2430,12 @@ ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
 		tsk = tsk->group_leader;
 
 	/*
-	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become
-	 * trapped in a cpuset, or RT worker may be born in a cgroup
-	 * with no rt_runtime allocated.  Just say no.
+	 * kthreads may acquire PF_NO_SETAFFINITY during initialization.
+	 * If userland migrates such a kthread to a non-root cgroup, it can
+	 * become trapped in a cpuset, or RT kthread may be born in a
+	 * cgroup with no rt_runtime allocated.  Just say no.
 	 */
-	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
+	if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
 		ret = -EINVAL;
 		goto out_unlock_rcu;
 	}
@@ -2575,7 +2581,7 @@ restart:
 			if (!css || !percpu_ref_is_dying(&css->refcnt))
 				continue;
 
-			cgroup_get(dsct);
+			cgroup_get_live(dsct);
 			prepare_to_wait(&dsct->offline_waitq, &wait,
 					TASK_UNINTERRUPTIBLE);
 
@@ -3946,7 +3952,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
 {
 	lockdep_assert_held(&cgroup_mutex);
 
-	cgroup_get(cgrp);
+	cgroup_get_live(cgrp);
 
 	memset(css, 0, sizeof(*css));
 	css->cgroup = cgrp;
@@ -4122,7 +4128,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	/* allocation complete, commit to creation */
 	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
 	atomic_inc(&root->nr_cgrps);
-	cgroup_get(parent);
+	cgroup_get_live(parent);
 
 	/*
 	 * @cgrp is now fully operational.  If something fails after this
@@ -4512,7 +4518,7 @@ int __init cgroup_init(void)
 	hash_add(css_set_table, &init_css_set.hlist,
 		 css_set_hash(init_css_set.subsys));
 
-	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
+	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0, 0));
 
 	mutex_unlock(&cgroup_mutex);
 
@@ -4946,7 +4952,7 @@ struct cgroup *cgroup_get_from_path(const char *path)
 	if (kn) {
 		if (kernfs_type(kn) == KERNFS_DIR) {
 			cgrp = kn->priv;
-			cgroup_get(cgrp);
+			cgroup_get_live(cgrp);
 		} else {
 			cgrp = ERR_PTR(-ENOTDIR);
 		}
@@ -5026,6 +5032,11 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
 
 	/* Socket clone path */
 	if (skcd->val) {
+		/*
+		 * We might be cloning a socket which is left in an empty
+		 * cgroup and the cgroup might have already been rmdir'd.
+		 * Don't use cgroup_get_live().
+		 */
 		cgroup_get(sock_cgroup_ptr(skcd));
 		return;
 	}