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

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Message-ID: <20181116055551.zxfydbpoicslsfkg@gondor.apana.org.au>
Date:   Fri, 16 Nov 2018 13:55:51 +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] rhashtable: detect when object movement between tables
 might have invalidated a lookup

On Thu, Nov 15, 2018 at 10:32:13AM +1100, NeilBrown wrote:
>
> +#define	RHT_NULLS_MARKER(ptr)	\
> +	((void *)NULLS_MARKER(((unsigned long) (ptr)) >> 1))
>  #define INIT_RHT_NULLS_HEAD(ptr)	\
> -	((ptr) = (typeof(ptr)) NULLS_MARKER(0))
> +	((ptr) = RHT_NULLS_MARKER(&(ptr)))

Why are you shifting this by one?

> 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;

I don't understand why you can't continue to do NULLS_MARKER(0) or
RHT_NULLS_MARKER(0).

Cheers,
-- 
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