linux-kernel - Re: [PATCH] zonefs: remove unnecessary kobject

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Date:   Wed, 12 Apr 2023 17:04:16 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     Yangtao Li <frank.li@...o.com>,
        Naohiro Aota <naohiro.aota@....com>,
        Johannes Thumshirn <jth@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zonefs: remove unnecessary kobject_del()

On 4/12/23 12:19, Yangtao Li wrote:
> kobject_put() actually covers kobject removal automatically, which is
> single stage removal. So kill kobject_del() directly.
> 
> Signed-off-by: Yangtao Li <frank.li@...o.com>
> ---
>  fs/zonefs/sysfs.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/fs/zonefs/sysfs.c b/fs/zonefs/sysfs.c
> index 8ccb65c2b419..a535bdea1097 100644
> --- a/fs/zonefs/sysfs.c
> +++ b/fs/zonefs/sysfs.c
> @@ -113,7 +113,6 @@ void zonefs_sysfs_unregister(struct super_block *sb)
>  	if (!sbi || !sbi->s_sysfs_registered)
>  		return;
>  
> -	kobject_del(&sbi->s_kobj);
>  	kobject_put(&sbi->s_kobj);
>  	wait_for_completion(&sbi->s_kobj_unregister);
>  }

What I am not sure about here is that if CONFIG_DEBUG_KOBJECT_RELEASE is
enabled, the kobj release is delayed, so the kobject will stay in sysfs
potentially after the umount() returns. Not exactly nice as that potentially
create races in user space... Not 100% sure though.

Greg ? Any thoughts on this ?