linux-kernel - Re: [PATCH] sysfs: kill an extra put in sysfs_create

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Date:	Wed, 18 Jul 2007 23:57:44 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Satyam Sharma <satyam.sharma@...il.com>
CC:	Gabriel C <nix.or.die@...glemail.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <clameter@....com>, gregkh@...e.de,
	miles.lane@...il.com
Subject: Re: [PATCH] sysfs: kill an extra put in sysfs_create_link() failure
 path

Satyam Sharma wrote:
> On 7/18/07, Tejun Heo <htejun@...il.com> wrote:
>> There is a subtle bug in sysfs_create_link() failure path.  When
>> symlink creation fails because there's already a node with the same
>> name, the target sysfs_dirent is put twice - once by failure path of
>> sysfs_create_link() and once more when the symlink is released.
> 
> The "symlink" is released? But the creation of the symlink is
> precisely what failed here ... did it not?
> 
>> Fix it by making only the symlink node responsible for putting
>> target_sd.
> 
> And again ... the changelog sounds confusing indeed, perhaps I'm
> not familiar enough with sysfs symlink-related terminology/semantics.
> Care to elaborate?
> 
>>         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
>>         if (!sd)
>>                 goto out_put;
>> +
>>         sd->s_elem.symlink.target_sd = target_sd;
>> +       target_sd = NULL;       /* reference is now owned by the
>> symlink */
> 
> Wow. This looks like a very mysterious way to fix a mysterious bug :-)
> BTW I just looked over at sysfs_create_link() and ... it looks quite ...
> unnecessarily complicated/obfuscated ...

Well, I dunno.  Probably my taste just sucks.  Please feel free to
submit patches and/or suggest better ideas.

-- 
tejun
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