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

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Message-ID: <589f6665-824f-bf08-3458-d3986d88f7fc@linux.alibaba.com>
Date:   Thu, 6 Apr 2023 18:55:40 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 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@...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.

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