netdev - Re: [PATCH 3/8] rhashtable: use cmpxchg() to protect ->future

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Date:   Sat, 5 May 2018 17:27:25 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     NeilBrown <neilb@...e.com>
Cc:     Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] rhashtable: use cmpxchg() to protect ->future_tbl.

On Fri, May 04, 2018 at 01:54:14PM +1000, NeilBrown wrote:
> Rather than borrowing one of the bucket locks to
> protect ->future_tbl updates, use cmpxchg().
> This gives more freedom to change how bucket locking
> is implemented.
> 
> Signed-off-by: NeilBrown <neilb@...e.com>

This looks nice.

> -	spin_unlock_bh(old_tbl->locks);
> +	rcu_assign_pointer(tmp, new_tbl);

Do we need this barrier since cmpxchg is supposed to provide memory
barrier semantics?

> +	if (cmpxchg(&old_tbl->future_tbl, NULL, tmp) != NULL)
> +		return -EEXIST;

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