Re: [PoC 2/7] Add kobject to super_block

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Apr 28, 2016 at 09:01:17PM -0500, Goldwyn Rodrigues wrote:
> @@ -167,7 +204,8 @@ static void destroy_super(struct super_block *s)
>  	WARN_ON(!list_empty(&s->s_mounts));
>  	kfree(s->s_subtype);
>  	kfree(s->s_options);
> -	call_rcu(&s->rcu, destroy_super_rcu);
> +	if (s->s_type->fs_flags & FS_CREATE_SYSFS)
> +		kobject_del(&s->s_kobj);

So we have kobject_del() under a spinlock.  Wonderful...  Better yet,
you have the sodding kobjects sitting around well past the point when
the filesystem driver has gone through rmmod.

sysfs: lifetime rules made simple.  So simple that they don't fit a lot of
situations, but hey - it sure *looks* easy to use...

NAK.  If you want a description of super_block life cycle, I can describe it
to you.  But please, don't play with it until you understand it.