memcg_write_event_control(): switch to CLASS(fd)

some reordering required - take both fdget() to the point before
the allocations, with matching move of fdput() to the very end
of failure exit(s); after that it converts trivially.

simplify the cleanups that involve css_put(), while we are at it...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

mm/memcontrol-v1.c

@@ -1911,8 +1911,6 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	struct mem_cgroup_event *event;
 	struct cgroup_subsys_state *cfile_css;
 	unsigned int efd, cfd;
-	struct fd efile;
-	struct fd cfile;
 	struct dentry *cdentry;
 	const char *name;
 	char *endp;
@@ -1936,6 +1934,12 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	else
 		return -EINVAL;
 
+	CLASS(fd, efile)(efd);
+	if (fd_empty(efile))
+		return -EBADF;
+
+	CLASS(fd, cfile)(cfd);
+
 	event = kzalloc(sizeof(*event), GFP_KERNEL);
 	if (!event)
 		return -ENOMEM;
@@ -1946,20 +1950,13 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	init_waitqueue_func_entry(&event->wait, memcg_event_wake);
 	INIT_WORK(&event->remove, memcg_event_remove);
 
-	efile = fdget(efd);
-	if (!fd_file(efile)) {
-		ret = -EBADF;
-		goto out_kfree;
-	}
-
 	event->eventfd = eventfd_ctx_fileget(fd_file(efile));
 	if (IS_ERR(event->eventfd)) {
 		ret = PTR_ERR(event->eventfd);
-		goto out_put_efile;
+		goto out_kfree;
 	}
 
-	cfile = fdget(cfd);
-	if (!fd_file(cfile)) {
+	if (fd_empty(cfile)) {
 		ret = -EBADF;
 		goto out_put_eventfd;
 	}
@@ -1968,7 +1965,7 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	/* AV: shouldn't we check that it's been opened for read instead? */
 	ret = file_permission(fd_file(cfile), MAY_READ);
 	if (ret < 0)
-		goto out_put_cfile;
+		goto out_put_eventfd;
 
 	/*
 	 * The control file must be a regular cgroup1 file. As a regular cgroup
@@ -1977,7 +1974,7 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	cdentry = fd_file(cfile)->f_path.dentry;
 	if (cdentry->d_sb->s_type != &cgroup_fs_type || !d_is_reg(cdentry)) {
 		ret = -EINVAL;
-		goto out_put_cfile;
+		goto out_put_eventfd;
 	}
 
 	/*
@@ -2010,7 +2007,7 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 		event->unregister_event = memsw_cgroup_usage_unregister_event;
 	} else {
 		ret = -EINVAL;
-		goto out_put_cfile;
+		goto out_put_eventfd;
 	}
 
 	/*
@@ -2022,11 +2019,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 					       &memory_cgrp_subsys);
 	ret = -EINVAL;
 	if (IS_ERR(cfile_css))
-		goto out_put_cfile;
-	if (cfile_css != css) {
-		css_put(cfile_css);
-		goto out_put_cfile;
-	}
+		goto out_put_eventfd;
+	if (cfile_css != css)
+		goto out_put_css;
 
 	ret = event->register_event(memcg, event->eventfd, buf);
 	if (ret)
@@ -2037,23 +2032,14 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 	spin_lock_irq(&memcg->event_list_lock);
 	list_add(&event->list, &memcg->event_list);
 	spin_unlock_irq(&memcg->event_list_lock);
-
-	fdput(cfile);
-	fdput(efile);
-
 	return nbytes;
 
 out_put_css:
-	css_put(css);
-out_put_cfile:
-	fdput(cfile);
+	css_put(cfile_css);
 out_put_eventfd:
 	eventfd_ctx_put(event->eventfd);
-out_put_efile:
-	fdput(efile);
 out_kfree:
 	kfree(event);
-
 	return ret;
 }