Re: [PATCH v5 1/4] cgroup: implement eventfd-based generic API for notifications

[Li Zefan <lizf@cn.fujitsu.com>]

Kirill A. Shutemov wrote:
> On Thu, Jan 7, 2010 at 3:01 AM, Paul Menage <menage@google.com> wrote:
>> On Wed, Dec 30, 2009 at 7:57 AM, Kirill A. Shutemov
>> <kirill@shutemov.name> wrote:
>>> +
>>> +       if (!IS_ERR(efile))
>>> +               fput(efile);
>> While this is OK currently, it's a bit fragile. efile starts as NULL,
>> and IS_ERR(NULL) is false. So if we jump to fail: before trying to do
>> the eventfd_fget() then we'll try to fput(NULL), which will oops. This
>> works because we don't currently jump to fail: until after
>> eventfd_fget(), but someone could add an extra setup step between the
>> kzalloc() and the eventfd_fget() which could fail.
> 
> So we need to use IS_ERR_OR_NULL here instread of IS_ERR, don't we?
> 

Use multi labels is much better:

label4::
	fput(cfile);
label3:
	eventfd_ctx_put(event->eventfd);
label2:
	fput(efile);
label1:
	kfree(event);

compared to:

+fail:
+	if (!IS_ERR(cfile))
+		fput(cfile);
+
+	if (event && event->eventfd && !IS_ERR(event->eventfd))
+		eventfd_ctx_put(event->eventfd);
+
+	if (!IS_ERR(efile))
+		fput(efile);
+
+	kfree(event);