diff mbox series

[07/18] rhashtable: use cmpxchg() to protect ->future_tbl.

Message ID 152782824954.30340.10107132482367263068.stgit@noble
State RFC, archived
Delegated to: David Miller
Headers show
Series Assorted rhashtable improvements | expand

Commit Message

NeilBrown June 1, 2018, 4:44 a.m. UTC 
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@suse.com>
---
 lib/rhashtable.c |   15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

Comments

Herbert Xu June 1, 2018, 4:44 p.m. UTC | #1 
On Fri, Jun 01, 2018 at 02:44:09PM +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@suse.com>

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
diff mbox series

Patch

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index e209069f1d74..b5d17bce19ff 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -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;
 }