rhashtable: Add multiple rehash support

This patch adds the missing bits to allow multiple rehashes.  The
read-side as well as remove already handle this correctly.  So it's
only the rehasher and insertion that need modification to handle
this.

Note that this patch doesn't actually enable it so for now rehashing
is still only performed by the worker thread.

This patch also disables the explicit expand/shrink interface because
the table is meant to expand and shrink automatically, and continuing
to export these interfaces unnecessarily complicates the life of the
rehasher since the rehash process is now composed of two parts.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 12 deletions

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index bc2488b98321..e8ffcdb5e239 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -308,9 +308,6 @@ int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 			   struct rhash_head *obj,
 			   struct bucket_table *old_tbl);
 
-int rhashtable_expand(struct rhashtable *ht);
-int rhashtable_shrink(struct rhashtable *ht);
-
 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter);
 void rhashtable_walk_exit(struct rhashtable_iter *iter);
 int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
@@ -541,17 +538,22 @@ static inline int __rhashtable_insert_fast(
 	rcu_read_lock();
 
 	tbl = rht_dereference_rcu(ht->tbl, ht);
-	hash = rht_head_hashfn(ht, tbl, obj, params);
-	lock = rht_bucket_lock(tbl, hash);
-
-	spin_lock_bh(lock);
 
-	/* Because we have already taken the bucket lock in tbl,
-	 * if we find that future_tbl is not yet visible then
-	 * that guarantees all other insertions of the same entry
-	 * will also grab the bucket lock in tbl because until
-	 * the rehash completes ht->tbl won't be changed.
+	/* All insertions must grab the oldest table containing
+	 * the hashed bucket that is yet to be rehashed.
 	 */
+	for (;;) {
+		hash = rht_head_hashfn(ht, tbl, obj, params);
+		lock = rht_bucket_lock(tbl, hash);
+		spin_lock_bh(lock);
+
+		if (tbl->rehash <= hash)
+			break;
+
+		spin_unlock_bh(lock);
+		tbl = rht_dereference_rcu(tbl->future_tbl, ht);
+	}
+
 	new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 	if (unlikely(new_tbl)) {
 		err = rhashtable_insert_slow(ht, key, obj, new_tbl);