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

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Message-ID: <cc557aab1001070436w446ef85n55dd2af5e733f55e@mail.gmail.com>
Date:	Thu, 7 Jan 2010 14:36:29 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Paul Menage <menage@...gle.com>
Cc:	containers@...ts.linux-foundation.org, linux-mm@...ck.org,
	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Dan Malek <dan@...eddedalley.com>,
	Vladislav Buzov <vbuzov@...eddedalley.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Alexander Shishkin <virtuoso@...nd.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/4] cgroup: implement eventfd-based generic API for 
	notifications

On Thu, Jan 7, 2010 at 3:01 AM, Paul Menage <menage@...gle.com> wrote:
> On Wed, Dec 30, 2009 at 7:57 AM, Kirill A. Shutemov
> <kirill@...temov.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?
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