Re: [PATCH 2/3] erofs: convert to use kobject_is_added()

[Gao Xiang]

On 2023/4/6 18:27, Greg KH wrote:
> On Thu, Apr 06, 2023 at 06:13:05PM +0800, Gao Xiang wrote:
> > Hi Greg,
> >
> > On 2023/4/6 18:03, Greg KH wrote:
> > > On Thu, Apr 06, 2023 at 05:30:55PM +0800, Yangtao Li wrote:
> > > > Use kobject_is_added() instead of directly accessing the internal
> > > > variables of kobject. BTW kill kobject_del() directly, because
> > > > kobject_put() actually covers kobject removal automatically.
> > > >
> > > > Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
> > > > ---
> > > >    fs/erofs/sysfs.c | 3 +--
> > > >    1 file changed, 1 insertion(+), 2 deletions(-)
> > > >
> > > > diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
> > > > index 435e515c0792..daac23e32026 100644
> > > > --- a/fs/erofs/sysfs.c
> > > > +++ b/fs/erofs/sysfs.c
> > > > @@ -240,8 +240,7 @@ void erofs_unregister_sysfs(struct super_block *sb)
> > > >    {
> > > >    	struct erofs_sb_info *sbi = EROFS_SB(sb);
> > > > -	if (sbi->s_kobj.state_in_sysfs) {
> > > > -		kobject_del(&sbi->s_kobj);
> > > > +	if (kobject_is_added(&sbi->s_kobj)) {
> > >
> > > I do not understand why this check is even needed, I do not think it
> > > should be there at all as obviously the kobject was registered if it now
> > > needs to not be registered.
> >
> > I think Yangtao sent a new patchset which missed the whole previous
> > background discussions as below:
> > https://lore.kernel.org/r/028a1b56-72c9-75f6-fb68-1dc5181bf2e8@xxxxxxxxxxxxxxxxx
> >
> > It's needed because once a syzbot complaint as below:
> > https://lore.kernel.org/r/CAD-N9QXNx=p3-QoWzk6pCznF32CZy8kM3vvo8mamfZZ9CpUKdw@xxxxxxxxxxxxxx
> >
> > I'd suggest including the previous backgrounds at least in the newer patchset,
> > otherwise it makes me explain again and again...
>
> That would be good, as I do not think this is correct, it should be
> fixed in a different way, see my response to the zonefs patch in this
> series as a much simpler method to use.

Yes, but here (sbi->s_kobj) is not a kobject pointer (also at a quick
glance it seems that zonefs has similar code), and also we couldn't
just check the sbi is NULL or not here only, since sbi is already
non-NULL in this path and there are some others in sbi to free in
other functions.

s_kobj could be changed into a pointer if needed.  I'm all fine with
either way since as you said, it's a boilerplate filesystem kobject
logic duplicated from somewhere.  Hopefully Yangtao could help take
this task since he sent me patches about this multiple times.

Thanks,
Gao Xiang

> thanks,
>
> greg k-h