Re: [PATCH] sysfs: kill an extra put in sysfs_create_link() failure path

Miles Lane
2007-07-18T16:59:45Z

On 7/18/07, Satyam Sharma <satyam.sharma@gmail.com> wrote:
> On 7/18/07, Tejun Heo <htejun@gmail.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.

I tried to apply the patch you sent earlier, but it was rejected
(2.6.22-rc6-mm1 + Tejun's patch + your patch). When you and
Tejun agree on an additional patch, I'd be happy to test it for you.

Miles