Re: WARNING in kill_block_super

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

On Wed, Apr 04, 2018 at 07:53:07PM +0900, Tetsuo Handa wrote:
> Al and Michal, are you OK with this patch?

First of all, it does *NOT* fix the problems with careless ->kill_sb().
The fuse-blk case is the only real rationale so far.  Said that,

> @@ -166,6 +166,7 @@ static void destroy_unused_super(struct super_block *s)
>  	security_sb_free(s);
>  	put_user_ns(s->s_user_ns);
>  	kfree(s->s_subtype);
> +	kfree(s->s_shrink.nr_deferred);

is probably better done with an inlined helper (fs/super.c has no business knowing
about ->nr_deferred name, and there probably will be other users of that
preallocation of yours).  And the same helper would be better off zeroing the
pointer, same as unregister_shrinker() does.


> -int register_shrinker(struct shrinker *shrinker)
> +int prepare_shrinker(struct shrinker *shrinker)

preallocate_shrinker(), perhaps?

> +int register_shrinker(struct shrinker *shrinker)
> +{
> +	int err = prepare_shrinker(shrinker);
> +
> +	if (err)
> +		return err;
> +	register_shrinker_prepared(shrinker);

	if (!err)
		register_....;
	return err;

would be better, IMO.