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Commit 0ad66449 authored by NeilBrown's avatar NeilBrown Committed by David S. Miller
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rhashtable: use cmpxchg() to protect ->future_tbl. 



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.

Acked-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5af68ef7

lib/rhashtable.c

+4 −11
Original line number Diff line number Diff line
@@ -297,21 +297,14 @@ static int rhashtable_rehash_attach(struct rhashtable *ht, 
				    struct bucket_table *old_tbl,

				    struct bucket_table *new_tbl)

{

	/* Protect future_tbl using the first bucket lock. */

	spin_lock_bh(old_tbl->locks);



	/* Did somebody beat us to it? */

	if (rcu_access_pointer(old_tbl->future_tbl)) {

		spin_unlock_bh(old_tbl->locks);

		return -EEXIST;

	}



	/* Make insertions go into the new, empty table right away. Deletions

	 * and lookups will be attempted in both tables until we synchronize.

	 * As cmpxchg() provides strong barriers, we do not need

	 * rcu_assign_pointer().

	 */

	rcu_assign_pointer(old_tbl->future_tbl, new_tbl);



	spin_unlock_bh(old_tbl->locks);

	if (cmpxchg(&old_tbl->future_tbl, NULL, new_tbl) != NULL)

		return -EEXIST;



	return 0;

}