linux-kernel - Re: [PATCH 2/3] erofs: convert to use kobject_is

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Message-ID: <2023040654-protrude-unlucky-f164@gregkh>
Date:   Thu, 6 Apr 2023 12:27:29 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc:     Yangtao Li <frank.li@...o.com>, xiang@...nel.org, chao@...nel.org,
        huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
        damien.lemoal@...nsource.wdc.com, naohiro.aota@....com,
        jth@...nel.org, rafael@...nel.org, linux-erofs@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] erofs: convert to use kobject_is_added()

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@...o.com>
> > > ---
> > >   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@linux.alibaba.com
> 
> It's needed because once a syzbot complaint as below:
> https://lore.kernel.org/r/CAD-N9QXNx=p3-QoWzk6pCznF32CZy8kM3vvo8mamfZZ9CpUKdw@mail.gmail.com
> 
> 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.

thanks,

greg k-h