Re: [PATCH] fs: handle shrinker registration failure in sget_userns

From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: jack@suse.cz, viro@zeniv.linux.org.uk, david@fromorbit.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	akpm@linux-foundation.org
Subject: Re: [PATCH] fs: handle shrinker registration failure in sget_userns
Date: Thu, 23 Nov 2017 15:06:00 +0100	[thread overview]
Message-ID: <20171123140600.kchjwercnkxc2xjb@dhcp22.suse.cz> (raw)
In-Reply-To: <201711232257.BFA41889.LOVOtFHFQJOSMF@I-love.SAKURA.ne.jp>

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