Revert "kernfs: restructure removal path to fix possible premature return"

This reverts commit 45a140e5.

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: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/dir.c

@@ -181,38 +181,14 @@ void kernfs_put_active(struct kernfs_node *kn)
  * kernfs_drain - drain kernfs_node
  * @kn: kernfs_node to drain
  *
- * Drain existing usages of @kn.  Mutiple removers may invoke this function
- * concurrently on @kn and all will return after draining is complete.
- * Returns %true if drain is performed and kernfs_mutex was temporarily
- * released.  %false if @kn was already drained and no operation was
- * necessary.
- *
- * The caller is responsible for ensuring @kn stays pinned while this
- * function is in progress even if it gets removed by someone else.
+ * Drain existing usages.
  */
-static bool kernfs_drain(struct kernfs_node *kn)
-	__releases(&kernfs_mutex) __acquires(&kernfs_mutex)
+static void kernfs_drain(struct kernfs_node *kn)
 {
 	struct kernfs_root *root = kernfs_root(kn);
 
-	lockdep_assert_held(&kernfs_mutex);
 	WARN_ON_ONCE(atomic_read(&kn->active) >= 0);
 
-	/*
-	 * We want to go through the active ref lockdep annotation at least
-	 * once for all node removals, but the lockdep annotation can't be
-	 * nested inside kernfs_mutex and deactivation can't make forward
-	 * progress if we keep dropping the mutex.  Use JUST_ACTIVATED to
-	 * force the slow path once for each deactivation if lockdep is
-	 * enabled.
-	 */
-	if ((!kernfs_lockdep(kn) || !(kn->flags & KERNFS_JUST_DEACTIVATED)) &&
-	    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
-		return false;
-
-	kn->flags &= ~KERNFS_JUST_DEACTIVATED;
-	mutex_unlock(&kernfs_mutex);
-
 	if (kernfs_lockdep(kn)) {
 		rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
 		if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
@@ -226,9 +202,6 @@ static bool kernfs_drain(struct kernfs_node *kn)
 		lock_acquired(&kn->dep_map, _RET_IP_);
 		rwsem_release(&kn->dep_map, 1, _RET_IP_);
 	}
-
-	mutex_lock(&kernfs_mutex);
-	return true;
 }
 
 /**
@@ -473,6 +446,49 @@ int kernfs_add_one(struct kernfs_addrm_cxt *acxt, struct kernfs_node *kn,
 	return 0;
 }
 
+/**
+ *	kernfs_remove_one - remove kernfs_node from parent
+ *	@acxt: addrm context to use
+ *	@kn: kernfs_node to be removed
+ *
+ *	Mark @kn removed and drop nlink of parent inode if @kn is a
+ *	directory.  @kn is unlinked from the children list.
+ *
+ *	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().
+ */
+static void kernfs_remove_one(struct kernfs_addrm_cxt *acxt,
+			      struct kernfs_node *kn)
+{
+	struct kernfs_iattrs *ps_iattr;
+
+	/*
+	 * Removal can be called multiple times on the same node.  Only the
+	 * first invocation is effective and puts the base ref.
+	 */
+	if (atomic_read(&kn->active) < 0)
+		return;
+
+	if (kn->parent) {
+		kernfs_unlink_sibling(kn);
+
+		/* Update timestamps on the parent */
+		ps_iattr = kn->parent->iattr;
+		if (ps_iattr) {
+			ps_iattr->ia_iattr.ia_ctime = CURRENT_TIME;
+			ps_iattr->ia_iattr.ia_mtime = CURRENT_TIME;
+		}
+	}
+
+	atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
+	kn->u.removed_list = acxt->removed;
+	acxt->removed = kn;
+}
+
 /**
  *	kernfs_addrm_finish - finish up kernfs_node add/remove
  *	@acxt: addrm context to finish up
@@ -496,6 +512,7 @@ void kernfs_addrm_finish(struct kernfs_addrm_cxt *acxt)
 
 		acxt->removed = kn->u.removed_list;
 
+		kernfs_drain(kn);
 		kernfs_unmap_bin_file(kn);
 		kernfs_put(kn);
 	}
@@ -805,73 +822,23 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 	return pos->parent;
 }
 
-static void __kernfs_deactivate(struct kernfs_node *kn)
-{
-	struct kernfs_node *pos;
-
-	lockdep_assert_held(&kernfs_mutex);
-
-	/* 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) {
-			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
-			pos->flags |= KERNFS_JUST_DEACTIVATED;
-		}
-	}
-
-	/*
-	 * Drain the subtree.  If kernfs_drain() blocked to drain, which is
-	 * indicated by %true return, it temporarily released kernfs_mutex
-	 * and the rbtree might have been modified inbetween breaking our
-	 * future walk.  Restart the walk after each %true return.
-	 */
-	pos = NULL;
-	while ((pos = kernfs_next_descendant_post(pos, kn))) {
-		bool drained;
-
-		kernfs_get(pos);
-		drained = kernfs_drain(pos);
-		kernfs_put(pos);
-		if (drained)
-			pos = NULL;
-	}
-}
-
 static void __kernfs_remove(struct kernfs_addrm_cxt *acxt,
 			    struct kernfs_node *kn)
 {
-	struct kernfs_node *pos;
-
-	lockdep_assert_held(&kernfs_mutex);
+	struct kernfs_node *pos, *next;
 
 	if (!kn)
 		return;
 
 	pr_debug("kernfs %s: removing\n", kn->name);
 
-	__kernfs_deactivate(kn);
-
-	/* unlink the subtree node-by-node */
+	next = NULL;
 	do {
-		struct kernfs_iattrs *ps_iattr;
-
-		pos = kernfs_leftmost_descendant(kn);
-
-		if (pos->parent) {
-			kernfs_unlink_sibling(pos);
-
-			/* update timestamps on the parent */
-			ps_iattr = pos->parent->iattr;
-			if (ps_iattr) {
-				ps_iattr->ia_iattr.ia_ctime = CURRENT_TIME;
-				ps_iattr->ia_iattr.ia_mtime = CURRENT_TIME;
-			}
-		}
-
-		pos->u.removed_list = acxt->removed;
-		acxt->removed = pos;
-	} while (pos != kn);
+		pos = next;
+		next = kernfs_next_descendant_post(pos, kn);
+		if (pos)
+			kernfs_remove_one(acxt, pos);
+	} while (next);
 }
 
 /**

include/linux/kernfs.h

@@ -37,7 +37,6 @@ enum kernfs_node_type {
 #define KERNFS_FLAG_MASK	~KERNFS_TYPE_MASK
 
 enum kernfs_node_flag {
-	KERNFS_JUST_DEACTIVATED	= 0x0010, /* used to aid lockdep annotation */
 	KERNFS_NS		= 0x0020,
 	KERNFS_HAS_SEQ_SHOW	= 0x0040,
 	KERNFS_HAS_MMAP		= 0x0080,