Revert "kernfs: fix get_active failure handling in kernfs_seq_*()"

This reverts commit d92d2e6b.

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/file.c

@@ -54,38 +54,6 @@ static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
 	return kn->attr.ops;
 }
 
-/*
- * As kernfs_seq_stop() is also called after kernfs_seq_start() or
- * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
- * a seq_file iteration which is fully initialized with an active reference
- * or an aborted kernfs_seq_start() due to get_active failure.  The
- * position pointer is the only context for each seq_file iteration and
- * thus the stop condition should be encoded in it.  As the return value is
- * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
- * choice to indicate get_active failure.
- *
- * Unfortunately, this is complicated due to the optional custom seq_file
- * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
- * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
- * custom seq_file operations and thus can't decide whether put_active
- * should be performed or not only on ERR_PTR(-ENODEV).
- *
- * This is worked around by factoring out the custom seq_stop() and
- * put_active part into kernfs_seq_stop_active(), skipping it from
- * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
- * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
- * that kernfs_seq_stop_active() is skipped only after get_active failure.
- */
-static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
-{
-	struct kernfs_open_file *of = sf->private;
-	const struct kernfs_ops *ops = kernfs_ops(of->kn);
-
-	if (ops->seq_stop)
-		ops->seq_stop(sf, v);
-	kernfs_put_active(of->kn);
-}
-
 static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
 {
 	struct kernfs_open_file *of = sf->private;
@@ -101,11 +69,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
 
 	ops = kernfs_ops(of->kn);
 	if (ops->seq_start) {
-		void *next = ops->seq_start(sf, ppos);
-		/* see the comment above kernfs_seq_stop_active() */
-		if (next == ERR_PTR(-ENODEV))
-			kernfs_seq_stop_active(sf, next);
-		return next;
+		return ops->seq_start(sf, ppos);
 	} else {
 		/*
 		 * The same behavior and code as single_open().  Returns
@@ -121,11 +85,7 @@ static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
 	const struct kernfs_ops *ops = kernfs_ops(of->kn);
 
 	if (ops->seq_next) {
-		void *next = ops->seq_next(sf, v, ppos);
-		/* see the comment above kernfs_seq_stop_active() */
-		if (next == ERR_PTR(-ENODEV))
-			kernfs_seq_stop_active(sf, next);
-		return next;
+		return ops->seq_next(sf, v, ppos);
 	} else {
 		/*
 		 * The same behavior and code as single_open(), always
@@ -139,9 +99,12 @@ static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
 static void kernfs_seq_stop(struct seq_file *sf, void *v)
 {
 	struct kernfs_open_file *of = sf->private;
+	const struct kernfs_ops *ops = kernfs_ops(of->kn);
 
-	if (v != ERR_PTR(-ENODEV))
-		kernfs_seq_stop_active(sf, v);
+	if (ops->seq_stop)
+		ops->seq_stop(sf, v);
+
+	kernfs_put_active(of->kn);
 	mutex_unlock(&of->mutex);
 }