1 files changed, 90 insertions, 122 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d9d82e96d67f..fe374f803b20 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -159,7 +159,7 @@ static bool cgrp_dfl_visible;
 static u16 cgrp_dfl_inhibit_ss_mask;
 
 /* some controllers are implicitly enabled on the default hierarchy */
-static unsigned long cgrp_dfl_implicit_ss_mask;
+static u16 cgrp_dfl_implicit_ss_mask;
 
 /* The list of hierarchy roots */
 LIST_HEAD(cgroup_roots);
@@ -178,13 +178,13 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
 static u64 css_serial_nr_next = 1;
 
 /*
- * These bitmask flags indicate whether tasks in the fork and exit paths have
- * fork/exit handlers to call. This avoids us having to do extra work in the
- * fork/exit path to check which subsystems have fork/exit callbacks.
+ * These bitmasks identify subsystems with specific features to avoid
+ * having to do iterative checks repeatedly.
  */
 static u16 have_fork_callback __read_mostly;
 static u16 have_exit_callback __read_mostly;
 static u16 have_free_callback __read_mostly;
+static u16 have_canfork_callback __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
@@ -195,9 +195,6 @@ struct cgroup_namespace init_cgroup_ns = {
 	.root_cset	= &init_css_set,
 };
 
-/* Ditto for the can_fork callback. */
-static u16 have_canfork_callback __read_mostly;
-
 static struct file_system_type cgroup2_fs_type;
 static struct cftype cgroup_base_files[];
 
@@ -1916,49 +1913,18 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
 }
 EXPORT_SYMBOL_GPL(task_cgroup_path);
 
-/* used to track tasks and other necessary states during migration */
-struct cgroup_taskset {
-	/* the src and dst cset list running through cset->mg_node */
-	struct list_head	src_csets;
-	struct list_head	dst_csets;
-
-	/* the subsys currently being processed */
-	int			ssid;
-
-	/*
-	 * Fields for cgroup_taskset_*() iteration.
-	 *
-	 * Before migration is committed, the target migration tasks are on
-	 * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
-	 * the csets on ->dst_csets.  ->csets point to either ->src_csets
-	 * or ->dst_csets depending on whether migration is committed.
-	 *
-	 * ->cur_csets and ->cur_task point to the current task position
-	 * during iteration.
-	 */
-	struct list_head	*csets;
-	struct css_set		*cur_cset;
-	struct task_struct	*cur_task;
-};
-
-#define CGROUP_TASKSET_INIT(tset)	(struct cgroup_taskset){	\
-	.src_csets		= LIST_HEAD_INIT(tset.src_csets),	\
-	.dst_csets		= LIST_HEAD_INIT(tset.dst_csets),	\
-	.csets			= &tset.src_csets,			\
-}
-
 /**
- * cgroup_taskset_add - try to add a migration target task to a taskset
+ * cgroup_migrate_add_task - add a migration target task to a migration context
  * @task: target task
- * @tset: target taskset
+ * @mgctx: target migration context
  *
- * Add @task, which is a migration target, to @tset.  This function becomes
- * noop if @task doesn't need to be migrated.  @task's css_set should have
- * been added as a migration source and @task->cg_list will be moved from
- * the css_set's tasks list to mg_tasks one.
+ * Add @task, which is a migration target, to @mgctx->tset.  This function
+ * becomes noop if @task doesn't need to be migrated.  @task's css_set
+ * should have been added as a migration source and @task->cg_list will be
+ * moved from the css_set's tasks list to mg_tasks one.
  */
-static void cgroup_taskset_add(struct task_struct *task,
-			       struct cgroup_taskset *tset)
+static void cgroup_migrate_add_task(struct task_struct *task,
+				    struct cgroup_mgctx *mgctx)
 {
 	struct css_set *cset;
 
@@ -1978,10 +1944,11 @@ static void cgroup_taskset_add(struct task_struct *task,
 
 	list_move_tail(&task->cg_list, &cset->mg_tasks);
 	if (list_empty(&cset->mg_node))
-		list_add_tail(&cset->mg_node, &tset->src_csets);
+		list_add_tail(&cset->mg_node,
+			      &mgctx->tset.src_csets);
 	if (list_empty(&cset->mg_dst_cset->mg_node))
-		list_move_tail(&cset->mg_dst_cset->mg_node,
-			       &tset->dst_csets);
+		list_add_tail(&cset->mg_dst_cset->mg_node,
+			      &mgctx->tset.dst_csets);
 }
 
 /**
@@ -2048,17 +2015,16 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
 
 /**
  * cgroup_taskset_migrate - migrate a taskset
- * @tset: taget taskset
- * @root: cgroup root the migration is taking place on
+ * @mgctx: migration context
  *
- * Migrate tasks in @tset as setup by migration preparation functions.
+ * Migrate tasks in @mgctx as setup by migration preparation functions.
  * This function fails iff one of the ->can_attach callbacks fails and
- * guarantees that either all or none of the tasks in @tset are migrated.
- * @tset is consumed regardless of success.
+ * guarantees that either all or none of the tasks in @mgctx are migrated.
+ * @mgctx is consumed regardless of success.
  */
-static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
-				  struct cgroup_root *root)
+static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
 {
+	struct cgroup_taskset *tset = &mgctx->tset;
 	struct cgroup_subsys *ss;
 	struct task_struct *task, *tmp_task;
 	struct css_set *cset, *tmp_cset;
@@ -2069,7 +2035,7 @@ static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
 		return 0;
 
 	/* check that we can legitimately attach to the cgroup */
-	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
 		if (ss->can_attach) {
 			tset->ssid = ssid;
 			ret = ss->can_attach(tset);
@@ -2105,7 +2071,7 @@ static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
 	 */
 	tset->csets = &tset->dst_csets;
 
-	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
 		if (ss->attach) {
 			tset->ssid = ssid;
 			ss->attach(tset);
@@ -2116,7 +2082,7 @@ static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
 	goto out_release_tset;
 
 out_cancel_attach:
-	do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
 		if (ssid == failed_ssid)
 			break;
 		if (ss->cancel_attach) {
@@ -2151,25 +2117,31 @@ bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
 
 /**
  * cgroup_migrate_finish - cleanup after attach
- * @preloaded_csets: list of preloaded css_sets
+ * @mgctx: migration context
  *
  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
  * those functions for details.
  */
-void cgroup_migrate_finish(struct list_head *preloaded_csets)
+void cgroup_migrate_finish(struct cgroup_mgctx *mgctx)
 {
+	LIST_HEAD(preloaded);
 	struct css_set *cset, *tmp_cset;
 
 	lockdep_assert_held(&cgroup_mutex);
 
 	spin_lock_irq(&css_set_lock);
-	list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
+
+	list_splice_tail_init(&mgctx->preloaded_src_csets, &preloaded);
+	list_splice_tail_init(&mgctx->preloaded_dst_csets, &preloaded);
+
+	list_for_each_entry_safe(cset, tmp_cset, &preloaded, mg_preload_node) {
 		cset->mg_src_cgrp = NULL;
 		cset->mg_dst_cgrp = NULL;
 		cset->mg_dst_cset = NULL;
 		list_del_init(&cset->mg_preload_node);
 		put_css_set_locked(cset);
 	}
+
 	spin_unlock_irq(&css_set_lock);
 }
 
@@ -2177,10 +2149,10 @@ void cgroup_migrate_finish(struct list_head *preloaded_csets)
  * cgroup_migrate_add_src - add a migration source css_set
  * @src_cset: the source css_set to add
  * @dst_cgrp: the destination cgroup
- * @preloaded_csets: list of preloaded css_sets
+ * @mgctx: migration context
  *
  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
- * @src_cset and add it to @preloaded_csets, which should later be cleaned
+ * @src_cset and add it to @mgctx->src_csets, which should later be cleaned
  * up by cgroup_migrate_finish().
  *
  * This function may be called without holding cgroup_threadgroup_rwsem
@@ -2191,7 +2163,7 @@ void cgroup_migrate_finish(struct list_head *preloaded_csets)
  */
 void cgroup_migrate_add_src(struct css_set *src_cset,
 			    struct cgroup *dst_cgrp,
-			    struct list_head *preloaded_csets)
+			    struct cgroup_mgctx *mgctx)
 {
 	struct cgroup *src_cgrp;
 
@@ -2219,33 +2191,35 @@ void cgroup_migrate_add_src(struct css_set *src_cset,
 	src_cset->mg_src_cgrp = src_cgrp;
 	src_cset->mg_dst_cgrp = dst_cgrp;
 	get_css_set(src_cset);
-	list_add(&src_cset->mg_preload_node, preloaded_csets);
+	list_add_tail(&src_cset->mg_preload_node, &mgctx->preloaded_src_csets);
 }
 
 /**
  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
- * @preloaded_csets: list of preloaded source css_sets
+ * @mgctx: migration context
  *
  * Tasks are about to be moved and all the source css_sets have been
- * preloaded to @preloaded_csets.  This function looks up and pins all
- * destination css_sets, links each to its source, and append them to
- * @preloaded_csets.
+ * preloaded to @mgctx->preloaded_src_csets.  This function looks up and
+ * pins all destination css_sets, links each to its source, and append them
+ * to @mgctx->preloaded_dst_csets.
  *
  * This function must be called after cgroup_migrate_add_src() has been
  * called on each migration source css_set.  After migration is performed
  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
- * @preloaded_csets.
+ * @mgctx.
  */
-int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
+int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
 {
-	LIST_HEAD(csets);
 	struct css_set *src_cset, *tmp_cset;
 
 	lockdep_assert_held(&cgroup_mutex);
 
 	/* look up the dst cset for each src cset and link it to src */
-	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
+	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
+				 mg_preload_node) {
 		struct css_set *dst_cset;
+		struct cgroup_subsys *ss;
+		int ssid;
 
 		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
 		if (!dst_cset)
@@ -2270,15 +2244,19 @@ int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
 		src_cset->mg_dst_cset = dst_cset;
 
 		if (list_empty(&dst_cset->mg_preload_node))
-			list_add(&dst_cset->mg_preload_node, &csets);
+			list_add_tail(&dst_cset->mg_preload_node,
+				      &mgctx->preloaded_dst_csets);
 		else
 			put_css_set(dst_cset);
+
+		for_each_subsys(ss, ssid)
+			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
+				mgctx->ss_mask |= 1 << ssid;
 	}
 
-	list_splice_tail(&csets, preloaded_csets);
 	return 0;
 err:
-	cgroup_migrate_finish(&csets);
+	cgroup_migrate_finish(mgctx);
 	return -ENOMEM;
 }
 
@@ -2286,7 +2264,7 @@ err:
  * cgroup_migrate - migrate a process or task to a cgroup
  * @leader: the leader of the process or the task to migrate
  * @threadgroup: whether @leader points to the whole process or a single task
- * @root: cgroup root migration is taking place on
+ * @mgctx: migration context
  *
  * Migrate a process or task denoted by @leader.  If migrating a process,
  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
@@ -2301,9 +2279,8 @@ err:
  * actually starting migrating.
  */
 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
-		   struct cgroup_root *root)
+		   struct cgroup_mgctx *mgctx)
 {
-	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
 	struct task_struct *task;
 
 	/*
@@ -2315,14 +2292,14 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
 	rcu_read_lock();
 	task = leader;
 	do {
-		cgroup_taskset_add(task, &tset);
+		cgroup_migrate_add_task(task, mgctx);
 		if (!threadgroup)
 			break;
 	} while_each_thread(leader, task);
 	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
 
-	return cgroup_taskset_migrate(&tset, root);
+	return cgroup_migrate_execute(mgctx);
 }
 
 /**
@@ -2336,7 +2313,7 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 		       bool threadgroup)
 {
-	LIST_HEAD(preloaded_csets);
+	DEFINE_CGROUP_MGCTX(mgctx);
 	struct task_struct *task;
 	int ret;
 
@@ -2348,8 +2325,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 	rcu_read_lock();
 	task = leader;
 	do {
-		cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
-				       &preloaded_csets);
+		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
 		if (!threadgroup)
 			break;
 	} while_each_thread(leader, task);
@@ -2357,11 +2333,11 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 	spin_unlock_irq(&css_set_lock);
 
 	/* prepare dst csets and commit */
-	ret = cgroup_migrate_prepare_dst(&preloaded_csets);
+	ret = cgroup_migrate_prepare_dst(&mgctx);
 	if (!ret)
-		ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
+		ret = cgroup_migrate(leader, threadgroup, &mgctx);
 
-	cgroup_migrate_finish(&preloaded_csets);
+	cgroup_migrate_finish(&mgctx);
 
 	if (!ret)
 		trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
@@ -2373,20 +2349,9 @@ static int cgroup_procs_write_permission(struct task_struct *task,
 					 struct cgroup *dst_cgrp,
 					 struct kernfs_open_file *of)
 {
-	const struct cred *cred = current_cred();
-	const struct cred *tcred = get_task_cred(task);
 	int ret = 0;
 
-	/*
-	 * even if we're attaching all tasks in the thread group, we only
-	 * need to check permissions on one of them.
-	 */
-	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
-	    !uid_eq(cred->euid, tcred->uid) &&
-	    !uid_eq(cred->euid, tcred->suid))
-		ret = -EACCES;
-
-	if (!ret && cgroup_on_dfl(dst_cgrp)) {
+	if (cgroup_on_dfl(dst_cgrp)) {
 		struct super_block *sb = of->file->f_path.dentry->d_sb;
 		struct cgroup *cgrp;
 		struct inode *inode;
@@ -2404,9 +2369,21 @@ static int cgroup_procs_write_permission(struct task_struct *task,
 			ret = inode_permission(inode, MAY_WRITE);
 			iput(inode);
 		}
+	} else {
+		const struct cred *cred = current_cred();
+		const struct cred *tcred = get_task_cred(task);
+
+		/*
+		 * even if we're attaching all tasks in the thread group,
+		 * we only need to check permissions on one of them.
+		 */
+		if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
+		    !uid_eq(cred->euid, tcred->uid) &&
+		    !uid_eq(cred->euid, tcred->suid))
+			ret = -EACCES;
+		put_cred(tcred);
 	}
 
-	put_cred(tcred);
 	return ret;
 }
 
@@ -2528,8 +2505,7 @@ static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
  */
 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
 {
-	LIST_HEAD(preloaded_csets);
-	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
+	DEFINE_CGROUP_MGCTX(mgctx);
 	struct cgroup_subsys_state *d_css;
 	struct cgroup *dsct;
 	struct css_set *src_cset;
@@ -2545,33 +2521,28 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
 		struct cgrp_cset_link *link;
 
 		list_for_each_entry(link, &dsct->cset_links, cset_link)
-			cgroup_migrate_add_src(link->cset, dsct,
-					       &preloaded_csets);
+			cgroup_migrate_add_src(link->cset, dsct, &mgctx);
 	}
 	spin_unlock_irq(&css_set_lock);
 
 	/* NULL dst indicates self on default hierarchy */
-	ret = cgroup_migrate_prepare_dst(&preloaded_csets);
+	ret = cgroup_migrate_prepare_dst(&mgctx);
 	if (ret)
 		goto out_finish;
 
 	spin_lock_irq(&css_set_lock);
-	list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
+	list_for_each_entry(src_cset, &mgctx.preloaded_src_csets, mg_preload_node) {
 		struct task_struct *task, *ntask;
 
-		/* src_csets precede dst_csets, break on the first dst_cset */
-		if (!src_cset->mg_src_cgrp)
-			break;
-
 		/* all tasks in src_csets need to be migrated */
 		list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
-			cgroup_taskset_add(task, &tset);
+			cgroup_migrate_add_task(task, &mgctx);
 	}
 	spin_unlock_irq(&css_set_lock);
 
-	ret = cgroup_taskset_migrate(&tset, cgrp->root);
+	ret = cgroup_migrate_execute(&mgctx);
 out_finish:
-	cgroup_migrate_finish(&preloaded_csets);
+	cgroup_migrate_finish(&mgctx);
 	percpu_up_write(&cgroup_threadgroup_rwsem);
 	return ret;
 }
@@ -4098,6 +4069,11 @@ err_free_css:
 	return ERR_PTR(err);
 }
 
+/*
+ * The returned cgroup is fully initialized including its control mask, but
+ * it isn't associated with its kernfs_node and doesn't have the control
+ * mask applied.
+ */
 static struct cgroup *cgroup_create(struct cgroup *parent)
 {
 	struct cgroup_root *root = parent->root;
@@ -4165,11 +4141,6 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 
 	cgroup_propagate_control(cgrp);
 
-	/* @cgrp doesn't have dir yet so the following will only create csses */
-	ret = cgroup_apply_control_enable(cgrp);
-	if (ret)
-		goto out_destroy;
-
 	return cgrp;
 
 out_cancel_ref:
@@ -4177,9 +4148,6 @@ out_cancel_ref:
 out_free_cgrp:
 	kfree(cgrp);
 	return ERR_PTR(ret);
-out_destroy:
-	cgroup_destroy_locked(cgrp);
-	return ERR_PTR(ret);
 }
 
 int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)