cgroup: store a reference to cgroup_ns into cgroup_fs_context

... and trim cgroup_do_mount() arguments (renaming it to cgroup_do_get_tree())
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/cgroup/cgroup-internal.h

@@ -42,6 +42,7 @@ extern void __init enable_debug_cgroup(void);
  */
 struct cgroup_fs_context {
 	struct cgroup_root	*root;
+	struct cgroup_namespace	*ns;
 	unsigned int	flags;			/* CGRP_ROOT_* flags */
 
 	/* cgroup1 bits */
@@ -212,8 +213,7 @@ void cgroup_free_root(struct cgroup_root *root);
 void init_cgroup_root(struct cgroup_fs_context *ctx);
 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask);
 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
-int cgroup_do_mount(struct fs_context *fc, unsigned long magic,
-			       struct cgroup_namespace *ns);
+int cgroup_do_get_tree(struct fs_context *fc);
 
 int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp);
 void cgroup_migrate_finish(struct cgroup_mgctx *mgctx);

kernel/cgroup/cgroup-v1.c

@@ -1145,7 +1145,6 @@ struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
  */
 static int cgroup1_root_to_use(struct fs_context *fc)
 {
-	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 	struct cgroup_root *root;
 	struct cgroup_subsys *ss;
@@ -1217,7 +1216,7 @@ static int cgroup1_root_to_use(struct fs_context *fc)
 		return cg_invalf(fc, "cgroup1: No subsys list or none specified");
 
 	/* Hierarchies may only be created in the initial cgroup namespace. */
-	if (ns != &init_cgroup_ns)
+	if (ctx->ns != &init_cgroup_ns)
 		return -EPERM;
 
 	root = kzalloc(sizeof(*root), GFP_KERNEL);
@@ -1235,12 +1234,11 @@ static int cgroup1_root_to_use(struct fs_context *fc)
 
 int cgroup1_get_tree(struct fs_context *fc)
 {
-	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 	int ret;
 
 	/* Check if the caller has permission to mount. */
-	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+	if (!ns_capable(ctx->ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 
 	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
@@ -1252,7 +1250,7 @@ int cgroup1_get_tree(struct fs_context *fc)
 	mutex_unlock(&cgroup_mutex);
 
 	if (!ret)
-		ret = cgroup_do_mount(fc, CGROUP_SUPER_MAGIC, ns);
+		ret = cgroup_do_get_tree(fc);
 
 	if (!ret && percpu_ref_is_dying(&ctx->root->cgrp.self.refcnt)) {
 		struct super_block *sb = fc->root->d_sb;

kernel/cgroup/cgroup.c

@@ -2036,13 +2036,17 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	return ret;
 }
 
-int cgroup_do_mount(struct fs_context *fc, unsigned long magic,
-		    struct cgroup_namespace *ns)
+int cgroup_do_get_tree(struct fs_context *fc)
 {
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 	bool new_sb = false;
+	unsigned long magic;
 	int ret = 0;
 
+	if (fc->fs_type == &cgroup2_fs_type)
+		magic = CGROUP2_SUPER_MAGIC;
+	else
+		magic = CGROUP_SUPER_MAGIC;
 	fc->root = kernfs_mount(fc->fs_type, fc->sb_flags, ctx->root->kf_root,
 				magic, &new_sb);
 	if (IS_ERR(fc->root))
@@ -2052,7 +2056,7 @@ int cgroup_do_mount(struct fs_context *fc, unsigned long magic,
 	 * In non-init cgroup namespace, instead of root cgroup's dentry,
 	 * we return the dentry corresponding to the cgroupns->root_cgrp.
 	 */
-	if (!ret && ns != &init_cgroup_ns) {
+	if (!ret && ctx->ns != &init_cgroup_ns) {
 		struct dentry *nsdentry;
 		struct super_block *sb = fc->root->d_sb;
 		struct cgroup *cgrp;
@@ -2060,7 +2064,7 @@ int cgroup_do_mount(struct fs_context *fc, unsigned long magic,
 		mutex_lock(&cgroup_mutex);
 		spin_lock_irq(&css_set_lock);
 
-		cgrp = cset_cgroup_from_root(ns->root_cset, ctx->root);
+		cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
 
 		spin_unlock_irq(&css_set_lock);
 		mutex_unlock(&cgroup_mutex);
@@ -2089,6 +2093,7 @@ static void cgroup_fs_context_free(struct fs_context *fc)
 
 	kfree(ctx->name);
 	kfree(ctx->release_agent);
+	put_cgroup_ns(ctx->ns);
 	kfree(ctx);
 }
 
@@ -2106,7 +2111,7 @@ static int cgroup_get_tree(struct fs_context *fc)
 	cgroup_get_live(&cgrp_dfl_root.cgrp);
 	ctx->root = &cgrp_dfl_root;
 
-	ret = cgroup_do_mount(fc, CGROUP2_SUPER_MAGIC, ns);
+	ret = cgroup_do_get_tree(fc);
 	if (!ret)
 		apply_cgroup_root_flags(ctx->flags);
 	return ret;
@@ -2144,6 +2149,8 @@ static int cgroup_init_fs_context(struct fs_context *fc)
 	if (!use_task_css_set_links)
 		cgroup_enable_task_cg_lists();
 
+	ctx->ns = current->nsproxy->cgroup_ns;
+	get_cgroup_ns(ctx->ns);
 	fc->fs_private = ctx;
 	if (fc->fs_type == &cgroup2_fs_type)
 		fc->ops = &cgroup_fs_context_ops;