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Date:   Thu, 23 Nov 2017 12:26:54 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     syzbot 
        <bot+065a25551da6c9ab4283b7ae889c707a37ab2de3@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, hannes@...xchg.org,
        hillf.zj@...baba-inc.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mgorman@...hsingularity.net,
        minchan@...nel.org, shli@...com, syzkaller-bugs@...glegroups.com,
        ying.huang@...el.com, Al Viro <viro@...iv.linux.org.uk>,
        Dave Chinner <david@...morbit.com>
Subject: Re: general protection fault in __list_del_entry_valid (2)

On Tue 21-11-17 15:05:00, Michal Hocko wrote:
> [Cc Al and Dave - email thread starts http://lkml.kernel.org/r/001a113f996099503a055e793dd3@google.com]
[...]
> Something like the totally untested and possibly wrong
> ---
> diff --git a/fs/super.c b/fs/super.c
> index 994db21f59bf..1eb850413fdf 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -506,6 +506,11 @@ struct super_block *sget_userns(struct file_system_type *type,
>  		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
>  		if (!s)
>  			return ERR_PTR(-ENOMEM);
> +		if (register_shrinker(&s->s_shrink)) {
> +			up_write(&s->s_umount);
> +			destroy_super(s);
> +			return ERR_PTR(-ENOMEM);
> +		}
>  		goto retry;
>  	}
>  
> @@ -522,7 +527,6 @@ struct super_block *sget_userns(struct file_system_type *type,
>  	hlist_add_head(&s->s_instances, &type->fs_supers);
>  	spin_unlock(&sb_lock);
>  	get_filesystem(type);
> -	register_shrinker(&s->s_shrink);
>  	return s;
>  }

This is not complete. I thought we would unregister the shrinker
somewher in destroy_super path but this is not the case. I will send
another patch along with other shrinkers registration fixes in a
separate thread.

-- 
Michal Hocko
SUSE Labs

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