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

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Date:   Thu, 6 Apr 2023 18:13:05 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Yangtao Li <frank.li@...o.com>
Cc:     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()

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...

Thanks,
Gao Xiang

> 
> Meta-comment, we need to come up with a "filesystem kobject type" to get
> rid of lots of the boilerplate filesystem kobject logic as it's
> duplicated in every filesystem in tiny different ways and lots of times
> (like here), it's wrong.
> 
> kobjects were not designed to be "used raw" like this, ideally they
> would be wrapped in a subsystem that makes them easier to be used (like
> the driver model), but filesystems decided to use them and that usage
> just grew over the years.  That's evolution for you...> 
> thanks,
> 
> greg k-h