linux-kernel - Re: [PATCH v3] rhashtable: detect when object movement between tables might have invalidated a lookup

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Message-ID: <20181201084727.6mfh46yshxdoba4h@gondor.apana.org.au>
Date:   Sat, 1 Dec 2018 16:47:27 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     NeilBrown <neilb@...e.com>
Cc:     David Miller <davem@...emloft.net>, tgraf@...g.ch,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        eric.dumazet@...il.com
Subject: Re: [PATCH v3] rhashtable: detect when object movement between
 tables might have invalidated a lookup

On Fri, Nov 30, 2018 at 10:26:50AM +1100, NeilBrown wrote:
>
> diff --git a/lib/rhashtable.c b/lib/rhashtable.c
> index 30526afa8343..852ffa5160f1 100644
> --- a/lib/rhashtable.c
> +++ b/lib/rhashtable.c
> @@ -1179,8 +1179,7 @@ struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
>  					    unsigned int hash)
>  {
>  	const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
> -	static struct rhash_head __rcu *rhnull =
> -		(struct rhash_head __rcu *)NULLS_MARKER(0);
> +	static struct rhash_head __rcu *rhnull;
>  	unsigned int index = hash & ((1 << tbl->nest) - 1);
>  	unsigned int size = tbl->size >> tbl->nest;
>  	unsigned int subhash = hash;
> @@ -1198,8 +1197,11 @@ struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
>  		subhash >>= shift;
>  	}
>  
> -	if (!ntbl)
> +	if (!ntbl) {
> +		if (!rhnull)
> +			INIT_RHT_NULLS_HEAD(rhnull);
>  		return &rhnull;
> +	}

I think you missed my earlier reply beause of bouncing emails.

I think this is unnecessary because

	RHT_NULLS_MARKER(RHT_NULLS_MARKER(0)) = RHT_NULLS_MARKER(0)

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt