1 files changed, 117 insertions, 1 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 37dd6408f5f6..1aeb57969bff 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -396,6 +396,7 @@ 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;
@@ -461,6 +462,7 @@ 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);
@@ -561,6 +563,7 @@ 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;
 
@@ -773,7 +776,8 @@ 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 (atomic_read(&pos->active) >= 0) {
+		if (!pos->deact_depth++) {
+			WARN_ON_ONCE(atomic_read(&pos->active) < 0);
 			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
 			pos->flags |= KERNFS_JUST_DEACTIVATED;
 		}
@@ -797,6 +801,118 @@ 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);