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rhashtable: use cmpxchg() to protect ->future_tbl.

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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: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
NeilBrown 2018-06-18 12:52:50 +10:00 committed by David S. Miller
parent 5af68ef733
commit 0ad66449aa
1 changed files with 4 additions and 11 deletions
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15
lib/rhashtable.c
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@ -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;
}