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Date:   Thu, 23 Nov 2017 15:06:00 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     jack@...e.cz, viro@...iv.linux.org.uk, david@...morbit.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] fs: handle shrinker registration failure in sget_userns

On Thu 23-11-17 22:57:06, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > > @@ -260,9 +261,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
> > >  	s->s_shrink.count_objects = super_cache_count;
> > >  	s->s_shrink.batch = 1024;
> > >  	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
> > > -	INIT_LIST_HEAD(&s->s_shrink.list);
> > > -	return s;
> > > -
> > > +	if (register_shrinker(&s->s_shrink) == 0)
> > > +		return s;
> > >  fail:
> > >  	destroy_unused_super(s);
> > >  	return NULL;
> > 
> > But I am not sure this is correct. So what protects shrinker invocation
> > while the object is not initialized yet?
> 
> Then, what protects shrinker invocation in your patch?

It is s_umount lock but that one is alreay held at the point where you
suggested register_shrinker. My bad, I could have noticed that. Feel
free to take over and send a patch. Considering I've screwed several
times already I do not feel I am the right one to send the fix.

-- 
Michal Hocko
SUSE Labs

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