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

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Date:	Wed, 18 Jul 2007 20:18:40 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Tejun Heo" <htejun@...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

Hi Tejun,

Thanks for tracking this down and fixing it.

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 ...

Thanks again,
Satyam
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