On 03/10/15 at 09:27am, Herbert Xu wrote:

This patch adds a rehash function that supports the use of any
hash function for the new table.  This is needed to support changing
the random seed value during the lifetime of the hash table.

However for now the random seed value is still constant and the
rehash function is simply used to replace the existing expand/shrink
functions.

Signed-off-by: Herbert Xu <redacted>

+static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
+	struct bucket_table *new_tbl = rht_dereference(ht->future_tbl, ht);
+	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];

[...]

I absolutely love the simplification this brings. Looks great. I now
also understand what you meant with entry for entry rehashing.

+static void rhashtable_rehash(struct rhashtable *ht,
+			      struct bucket_table *new_tbl)
 {
-	ASSERT_BUCKET_LOCK(ht, new_tbl, new_hash);
+	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
+	unsigned old_hash;
+
+	get_random_bytes(&new_tbl->hash_rnd, sizeof(new_tbl->hash_rnd));
+
+	/* Make insertions go into the new, empty table right away. Deletions
+	 * and lookups will be attempted in both tables until we synchronize.
+	 * The synchronize_rcu() guarantees for the new table to be picked up
+	 * so no new additions go into the old table while we relink.
+	 */
+	rcu_assign_pointer(ht->future_tbl, new_tbl);

I think you need an rcu_synchronize() here. rhashtable_remove() must
be guaranteed to either see tbl != old_tbl and thus consider both
tables or the rehashing must be guaranteed to not start for an already
started removal. 

-static void __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
-				struct bucket_table *tbl,
-				const struct bucket_table *old_tbl, u32 hash)
+bool __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
+			 bool (*compare)(void *, void *), void *arg)

Why make this non-static? We already have rhashtable_lookup_compare_insert()
exported.

+bool __rhashtable_remove(struct rhashtable *ht, struct bucket_table *tbl,
+			 struct rhash_head *obj)

Same here.