Revert "kernfs: remove kernfs_addrm_cxt"

This reverts commit 99177a3411.

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

@@ -398,8 +398,29 @@ struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
 	return NULL;
 }
 
+/**
+ *	kernfs_addrm_start - prepare for kernfs_node add/remove
+ *	@acxt: pointer to kernfs_addrm_cxt to be used
+ *
+ *	This function is called when the caller is about to add or remove
+ *	kernfs_node.  This function acquires kernfs_mutex.  @acxt is used
+ *	to keep and pass context to other addrm functions.
+ *
+ *	LOCKING:
+ *	Kernel thread context (may sleep).  kernfs_mutex is locked on
+ *	return.
+ */
+void kernfs_addrm_start(struct kernfs_addrm_cxt *acxt)
+	__acquires(kernfs_mutex)
+{
+	memset(acxt, 0, sizeof(*acxt));
+
+	mutex_lock(&kernfs_mutex);
+}
+
 /**
  *	kernfs_add_one - add kernfs_node to parent without warning
+ *	@acxt: addrm context to use
  *	@kn: kernfs_node to be added
  *	@parent: the parent kernfs_node to add @kn to
  *
@@ -407,29 +428,34 @@ struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
  *	parent inode if @kn is a directory and link into the children list
  *	of the parent.
  *
+ *	This function should be called between calls to
+ *	kernfs_addrm_start() and kernfs_addrm_finish() and should be passed
+ *	the same @acxt as passed to kernfs_addrm_start().
+ *
+ *	LOCKING:
+ *	Determined by kernfs_addrm_start().
+ *
  *	RETURNS:
  *	0 on success, -EEXIST if entry with the given name already
  *	exists.
  */
-int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
+int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn,
+		  struct kernfs_node *parent)
 {
+	bool has_ns = kernfs_ns_enabled(parent);
 	struct kernfs_iattrs *ps_iattr;
-	bool has_ns;
 	int ret;
 
-	if (!kernfs_get_active(parent))
-		return -ENOENT;
+	WARN_ON_ONCE(atomic_read(&parent->active) < 0);
 
-	mutex_lock(&kernfs_mutex);
-
-	ret = -EINVAL;
-	has_ns = kernfs_ns_enabled(parent);
-	if (WARN(has_ns != (bool)kn->ns, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
-		 has_ns ? "required" : "invalid", parent->name, kn->name))
-		goto out_unlock;
+	if (has_ns != (bool)kn->ns) {
+		WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
+		     has_ns ? "required" : "invalid", parent->name, kn->name);
+		return -EINVAL;
+	}
 
 	if (kernfs_type(parent) != KERNFS_DIR)
-		goto out_unlock;
+		return -EINVAL;
 
 	kn->hash = kernfs_name_hash(kn->name, kn->ns);
 	kn->parent = parent;
@@ -437,7 +463,7 @@ int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent)
 
 	ret = kernfs_link_sibling(kn);
 	if (ret)
-		goto out_unlock;
+		return ret;
 
 	/* Update timestamps on the parent */
 	ps_iattr = parent->iattr;
@@ -448,11 +474,34 @@ 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);
-	ret = 0;
-out_unlock:
+	return 0;
+}
+
+/**
+ *	kernfs_addrm_finish - finish up kernfs_node add/remove
+ *	@acxt: addrm context to finish up
+ *
+ *	Finish up kernfs_node add/remove.  Resources acquired by
+ *	kernfs_addrm_start() are released and removed kernfs_nodes are
+ *	cleaned up.
+ *
+ *	LOCKING:
+ *	kernfs_mutex is released.
+ */
+void kernfs_addrm_finish(struct kernfs_addrm_cxt *acxt)
+	__releases(kernfs_mutex)
+{
+	/* release resources acquired by kernfs_addrm_start() */
 	mutex_unlock(&kernfs_mutex);
-	kernfs_put_active(parent);
-	return ret;
+
+	/* kill removed kernfs_nodes */
+	while (acxt->removed) {
+		struct kernfs_node *kn = acxt->removed;
+
+		acxt->removed = kn->u.removed_list;
+
+		kernfs_put(kn);
+	}
 }
 
 /**
@@ -584,6 +633,7 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
 					 const char *name, umode_t mode,
 					 void *priv, const void *ns)
 {
+	struct kernfs_addrm_cxt acxt;
 	struct kernfs_node *kn;
 	int rc;
 
@@ -598,7 +648,14 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
 	kn->priv = priv;
 
 	/* link in */
-	rc = kernfs_add_one(kn, parent);
+	rc = -ENOENT;
+	if (kernfs_get_active(parent)) {
+		kernfs_addrm_start(&acxt);
+		rc = kernfs_add_one(&acxt, kn, parent);
+		kernfs_addrm_finish(&acxt);
+		kernfs_put_active(parent);
+	}
+
 	if (!rc)
 		return kn;
 
@@ -784,7 +841,8 @@ static void __kernfs_deactivate(struct kernfs_node *kn)
 	}
 }
 
-static void __kernfs_remove(struct kernfs_node *kn)
+static void __kernfs_remove(struct kernfs_addrm_cxt *acxt,
+			    struct kernfs_node *kn)
 {
 	struct kernfs_node *pos;
 
@@ -832,7 +890,8 @@ static void __kernfs_remove(struct kernfs_node *kn)
 				ps_iattr->ia_iattr.ia_mtime = CURRENT_TIME;
 			}
 
-			kernfs_put(pos);
+			pos->u.removed_list = acxt->removed;
+			acxt->removed = pos;
 		}
 
 		kernfs_put(pos);
@@ -847,9 +906,11 @@ static void __kernfs_remove(struct kernfs_node *kn)
  */
 void kernfs_remove(struct kernfs_node *kn)
 {
-	mutex_lock(&kernfs_mutex);
-	__kernfs_remove(kn);
-	mutex_unlock(&kernfs_mutex);
+	struct kernfs_addrm_cxt acxt;
+
+	kernfs_addrm_start(&acxt);
+	__kernfs_remove(&acxt, kn);
+	kernfs_addrm_finish(&acxt);
 }
 
 /**
@@ -864,6 +925,7 @@ void kernfs_remove(struct kernfs_node *kn)
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 			     const void *ns)
 {
+	struct kernfs_addrm_cxt acxt;
 	struct kernfs_node *kn;
 
 	if (!parent) {
@@ -872,13 +934,13 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 		return -ENOENT;
 	}
 
-	mutex_lock(&kernfs_mutex);
+	kernfs_addrm_start(&acxt);
 
 	kn = kernfs_find_ns(parent, name, ns);
 	if (kn)
-		__kernfs_remove(kn);
+		__kernfs_remove(&acxt, kn);
 
-	mutex_unlock(&kernfs_mutex);
+	kernfs_addrm_finish(&acxt);
 
 	if (kn)
 		return 0;

fs/kernfs/file.c

@@ -817,6 +817,7 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 					 bool name_is_static,
 					 struct lock_class_key *key)
 {
+	struct kernfs_addrm_cxt acxt;
 	struct kernfs_node *kn;
 	unsigned flags;
 	int rc;
@@ -852,7 +853,14 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 	if (ops->mmap)
 		kn->flags |= KERNFS_HAS_MMAP;
 
-	rc = kernfs_add_one(kn, parent);
+	rc = -ENOENT;
+	if (kernfs_get_active(parent)) {
+		kernfs_addrm_start(&acxt);
+		rc = kernfs_add_one(&acxt, kn, parent);
+		kernfs_addrm_finish(&acxt);
+		kernfs_put_active(parent);
+	}
+
 	if (rc) {
 		kernfs_put(kn);
 		return ERR_PTR(rc);

fs/kernfs/kernfs-internal.h

@@ -45,6 +45,13 @@ static inline struct kernfs_root *kernfs_root(struct kernfs_node *kn)
 	return kn->dir.root;
 }
 
+/*
+ * Context structure to be used while adding/removing nodes.
+ */
+struct kernfs_addrm_cxt {
+	struct kernfs_node	*removed;
+};
+
 /*
  * mount.c
  */
@@ -94,7 +101,10 @@ extern const struct inode_operations kernfs_dir_iops;
 
 struct kernfs_node *kernfs_get_active(struct kernfs_node *kn);
 void kernfs_put_active(struct kernfs_node *kn);
-int kernfs_add_one(struct kernfs_node *kn, struct kernfs_node *parent);
+void kernfs_addrm_start(struct kernfs_addrm_cxt *acxt);
+int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn,
+		   struct kernfs_node *parent);
+void kernfs_addrm_finish(struct kernfs_addrm_cxt *acxt);
 struct kernfs_node *kernfs_new_node(struct kernfs_root *root, const char *name,
 				    umode_t mode, unsigned flags);
 

fs/kernfs/symlink.c

@@ -27,6 +27,7 @@ struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 				       struct kernfs_node *target)
 {
 	struct kernfs_node *kn;
+	struct kernfs_addrm_cxt acxt;
 	int error;
 
 	kn = kernfs_new_node(kernfs_root(parent), name, S_IFLNK|S_IRWXUGO,
@@ -39,7 +40,14 @@ struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 	kn->symlink.target_kn = target;
 	kernfs_get(target);	/* ref owned by symlink */
 
-	error = kernfs_add_one(kn, parent);
+	error = -ENOENT;
+	if (kernfs_get_active(parent)) {
+		kernfs_addrm_start(&acxt);
+		error = kernfs_add_one(&acxt, kn, parent);
+		kernfs_addrm_finish(&acxt);
+		kernfs_put_active(parent);
+	}
+
 	if (!error)
 		return kn;
 

include/linux/kernfs.h

@@ -89,6 +89,10 @@ struct kernfs_node {
 
 	struct rb_node		rb;
 
+	union {
+		struct kernfs_node	*removed_list;
+	} u;
+
 	const void		*ns;	/* namespace tag */
 	unsigned int		hash;	/* ns + name hash */
 	union {