Revert "kernfs: implement kernfs_{de|re}activate[_self]()"

This reverts commit 9f010c2ad5.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/dir.c

@@ -396,7 +396,6 @@ struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
 
 	atomic_set(&kn->count, 1);
 	atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
-	kn->deact_depth = 1;
 	RB_CLEAR_NODE(&kn->rb);
 
 	kn->name = name;
@@ -462,7 +461,6 @@ int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
 
 	/* Mark the entry added into directory tree */
 	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
-	kn->deact_depth--;
 	ret = 0;
 out_unlock:
 	mutex_unlock(&kernfs_mutex);
@@ -563,7 +561,6 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
 	}
 
 	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
-	kn->deact_depth--;
 	kn->priv = priv;
 	kn->dir.root = root;
 
@@ -776,8 +773,7 @@ static void __kernfs_deactivate(struct kernfs_node *kn)
 	/* prevent any new usage under @kn by deactivating all nodes */
 	pos = NULL;
 	while ((pos = kernfs_next_descendant_post(pos, kn))) {
-		if (!pos->deact_depth++) {
+		if (atomic_read(&pos->active) >= 0) {
-			WARN_ON_ONCE(atomic_read(&pos->active) < 0);
 			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
 			pos->flags |= KERNFS_JUST_DEACTIVATED;
 		}
@@ -801,118 +797,6 @@ static void __kernfs_deactivate(struct kernfs_node *kn)
 	}
 }
 
-static void __kernfs_reactivate(struct kernfs_node *kn)
-{
-	struct kernfs_node *pos;
-
-	lockdep_assert_held(&kernfs_mutex);
-
-	pos = NULL;
-	while ((pos = kernfs_next_descendant_post(pos, kn))) {
-		if (!--pos->deact_depth) {
-			WARN_ON_ONCE(atomic_read(&pos->active) >= 0);
-			atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
-		}
-		WARN_ON_ONCE(pos->deact_depth < 0);
-	}
-
-	/* some nodes reactivated, kick get_active waiters */
-	wake_up_all(&kernfs_root(kn)->deactivate_waitq);
-}
-
-static void __kernfs_deactivate_self(struct kernfs_node *kn)
-{
-	/*
-	 * Take out ourself out of the active ref dependency chain and
-	 * deactivate.  If we're called without an active ref, lockdep will
-	 * complain.
-	 */
-	kernfs_put_active(kn);
-	__kernfs_deactivate(kn);
-}
-
-static void __kernfs_reactivate_self(struct kernfs_node *kn)
-{
-	__kernfs_reactivate(kn);
-	/*
-	 * Restore active ref dropped by deactivate_self() so that it's
-	 * balanced on return.  put_active() will soon be called on @kn, so
-	 * this can't break anything regardless of @kn's state.
-	 */
-	atomic_inc(&kn->active);
-	if (kernfs_lockdep(kn))
-		rwsem_acquire(&kn->dep_map, 0, 1, _RET_IP_);
-}
-
-/**
- * kernfs_deactivate - deactivate subtree of a node
- * @kn: kernfs_node to deactivate subtree of
- *
- * Deactivate the subtree of @kn.  On return, there's no active operation
- * going on under @kn and creation or renaming of a node under @kn is
- * blocked until @kn is reactivated or removed.  This function can be
- * called multiple times and nests properly.  Each invocation should be
- * paired with kernfs_reactivate().
- *
- * For a kernfs user which uses simple locking, the subsystem lock would
- * nest inside active reference.  This becomes problematic if the user
- * tries to remove nodes while holding the subystem lock as it would create
- * a reverse locking dependency from the subsystem lock to active ref.
- * This function can be used to break such reverse dependency.  The user
- * can call this function outside the subsystem lock and then proceed to
- * invoke kernfs_remove() while holding the subsystem lock without
- * introducing such reverse dependency.
- */
-void kernfs_deactivate(struct kernfs_node *kn)
-{
-	mutex_lock(&kernfs_mutex);
-	__kernfs_deactivate(kn);
-	mutex_unlock(&kernfs_mutex);
-}
-
-/**
- * kernfs_reactivate - reactivate subtree of a node
- * @kn: kernfs_node to reactivate subtree of
- *
- * Undo kernfs_deactivate().
- */
-void kernfs_reactivate(struct kernfs_node *kn)
-{
-	mutex_lock(&kernfs_mutex);
-	__kernfs_reactivate(kn);
-	mutex_unlock(&kernfs_mutex);
-}
-
-/**
- * kernfs_deactivate_self - deactivate subtree of a node from its own method
- * @kn: the self kernfs_node to deactivate subtree of
- *
- * The caller must be running off of a kernfs operation which is invoked
- * with an active reference - e.g. one of kernfs_ops.  Once this function
- * is called, @kn may be removed by someone else while the enclosing method
- * is in progress.  Other than that, this function is equivalent to
- * kernfs_deactivate() and should be paired with kernfs_reactivate_self().
- */
-void kernfs_deactivate_self(struct kernfs_node *kn)
-{
-	mutex_lock(&kernfs_mutex);
-	__kernfs_deactivate_self(kn);
-	mutex_unlock(&kernfs_mutex);
-}
-
-/**
- * kernfs_reactivate_self - reactivate subtree of a node from its own method
- * @kn: the self kernfs_node to reactivate subtree of
- *
- * Undo kernfs_deactivate_self().
- */
-void kernfs_reactivate_self(struct kernfs_node *kn)
-{
-	mutex_lock(&kernfs_mutex);
-	__kernfs_reactivate_self(kn);
-	mutex_unlock(&kernfs_mutex);
-}
-
 static void __kernfs_remove(struct kernfs_node *kn)
 {
 	struct kernfs_root *root = kernfs_root(kn);

include/linux/kernfs.h

@@ -80,8 +80,6 @@ struct kernfs_elem_attr {
 struct kernfs_node {
 	atomic_t		count;
 	atomic_t		active;
-	int			deact_depth;
-	unsigned int		hash;	/* ns + name hash */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
@@ -92,6 +90,7 @@ struct kernfs_node {
 	struct rb_node		rb;
 
 	const void		*ns;	/* namespace tag */
+	unsigned int		hash;	/* ns + name hash */
 	union {
 		struct kernfs_elem_dir		dir;
 		struct kernfs_elem_symlink	symlink;
@@ -234,10 +233,6 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 				       const char *name,
 				       struct kernfs_node *target);
-void kernfs_deactivate(struct kernfs_node *kn);
-void kernfs_reactivate(struct kernfs_node *kn);
-void kernfs_deactivate_self(struct kernfs_node *kn);
-void kernfs_reactivate_self(struct kernfs_node *kn);
 void kernfs_remove(struct kernfs_node *kn);
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 			     const void *ns);