configfs_readdir(): make safe under shared lock

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/configfs/dir.c

@@ -1633,11 +1633,9 @@ static int configfs_readdir(struct file *file, struct dir_context *ctx)
 
 	if (!dir_emit_dots(file, ctx))
 		return 0;
-	if (ctx->pos == 2) {
-		spin_lock(&configfs_dirent_lock);
+	spin_lock(&configfs_dirent_lock);
+	if (ctx->pos == 2)
 		list_move(q, &parent_sd->s_children);
-		spin_unlock(&configfs_dirent_lock);
-	}
 	for (p = q->next; p != &parent_sd->s_children; p = p->next) {
 		struct configfs_dirent *next;
 		const char *name;
@@ -1648,9 +1646,6 @@ static int configfs_readdir(struct file *file, struct dir_context *ctx)
 		if (!next->s_element)
 			continue;
 
-		name = configfs_get_name(next);
-		len = strlen(name);
-
 		/*
 		 * We'll have a dentry and an inode for
 		 * PINNED items and for open attribute
@@ -1664,7 +1659,6 @@ static int configfs_readdir(struct file *file, struct dir_context *ctx)
 		 * they close it.  Beyond that, we don't
 		 * care.
 		 */
-		spin_lock(&configfs_dirent_lock);
 		dentry = next->s_dentry;
 		if (dentry)
 			inode = d_inode(dentry);
@@ -1674,31 +1668,32 @@ static int configfs_readdir(struct file *file, struct dir_context *ctx)
 		if (!inode)
 			ino = iunique(sb, 2);
 
+		name = configfs_get_name(next);
+		len = strlen(name);
+
 		if (!dir_emit(ctx, name, len, ino, dt_type(next)))
 			return 0;
 
 		spin_lock(&configfs_dirent_lock);
 		list_move(q, p);
-		spin_unlock(&configfs_dirent_lock);
 		p = q;
 		ctx->pos++;
 	}
+	spin_unlock(&configfs_dirent_lock);
 	return 0;
 }
 
 static loff_t configfs_dir_lseek(struct file *file, loff_t offset, int whence)
 {
 	struct dentry * dentry = file->f_path.dentry;
 
-	inode_lock(d_inode(dentry));
 	switch (whence) {
 		case 1:
 			offset += file->f_pos;
 		case 0:
 			if (offset >= 0)
 				break;
 		default:
-			inode_unlock(d_inode(dentry));
 			return -EINVAL;
 	}
 	if (offset != file->f_pos) {
@@ -1724,7 +1719,6 @@ static loff_t configfs_dir_lseek(struct file *file, loff_t offset, int whence)
 			spin_unlock(&configfs_dirent_lock);
 		}
 	}
-	inode_unlock(d_inode(dentry));
 	return offset;
 }
 
@@ -1733,7 +1727,7 @@ const struct file_operations configfs_dir_operations = {
 	.release	= configfs_dir_close,
 	.llseek		= configfs_dir_lseek,
 	.read		= generic_read_dir,
-	.iterate	= configfs_readdir,
+	.iterate_shared	= configfs_readdir,
 };
 
 /**