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

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Date:	Wed, 18 Jul 2007 22:19:20 +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

On 7/18/07, Tejun Heo <htejun@...il.com> wrote:
> Tejun Heo wrote:
> > Satyam Sharma wrote:
> >>>> sysfs_find_dirent() -- to check for -EEXIST -- should be called
> >>>> *before* we create the new dentry for the to-be-created symlink
> >>>> in the first place. [ It's weird to grab a reference on the target
> >>>> for ourselves (and in fact even allocate the new dirent for the
> >>>> to-be-created symlink) and /then/ check for erroneous usage,
> >>>> and then go about undoing all that we should never have done
> >>>> at all. ] So this test could, and should, be made earlier, IMHO.
> >>> Locking.
> >> Well s/sysfs_find_dirent/sysfs_get_dirent/ then. And then simply put
> >> down the reference later.
> >
> > Isn't that the current code?
>
> Oops, somehow thought you were talking about allocating it first.
> Gee... what difference does using sysfs_get_dirent() make?  Do you think
> the following code is correct?
>
>         sd = sysfs_get_dirent("some name");
>         if (sd != NULL)
>                 return -EEXIST;
>         lock;
>         add_new_node("some name");
>         unlock;
>         sysfs_put_dirent(sd);

Nopes, it's not, of course. We'd need the parent's i_mutex as well
as the sysfs_mutex around both the EEXIST check as well as the
actual sysfs_add_one(), which is precisely what sysfs_addrm_start
and finish are, so you're right ... I'll factor this in.

Satyam
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