[PATCH] rhashtable: Restore insecure_elasticity toggle

[Herbert Xu]

Some users of rhashtable cannot handle insertion failures, and
are happy to accept the consequences of a hash table that having
very long chains.

Restore the insecure_elasticity toggle for these users.  In
addition to disabling the chain length checks, this also removes
the emergency resize that would otherwise occur when the hash
table occupancy hits 100% (an async resize is still scheduled
at 75%).

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

diff --git a/include/linux/rhashtable-types.h b/include/linux/rhashtable-types.h
index 015c8298bebc..72082428d6c6 100644
--- a/include/linux/rhashtable-types.h
+++ b/include/linux/rhashtable-types.h
@@ -49,6 +49,7 @@ typedef int (*rht_obj_cmpfn_t)(struct rhashtable_compare_arg *arg,
  * @head_offset: Offset of rhash_head in struct to be hashed
  * @max_size: Maximum size while expanding
  * @min_size: Minimum size while shrinking
+ * @insecure_elasticity: Set to true to disable chain length checks
  * @automatic_shrinking: Enable automatic shrinking of tables
  * @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
  * @obj_hashfn: Function to hash object
@@ -61,6 +62,7 @@ struct rhashtable_params {
 	u16			head_offset;
 	unsigned int		max_size;
 	u16			min_size;
+	bool			insecure_elasticity;
 	bool			automatic_shrinking;
 	rht_hashfn_t		hashfn;
 	rht_obj_hashfn_t	obj_hashfn;
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 0480509a6339..c793849d3f61 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -821,14 +821,15 @@ static __always_inline void *__rhashtable_insert_fast(
 		goto out;
 	}
 
-	if (elasticity <= 0)
+	if (elasticity <= 0 && !params->insecure_elasticity)
 		goto slow_path;
 
 	data = ERR_PTR(-E2BIG);
 	if (unlikely(rht_grow_above_max(ht, tbl)))
 		goto out_unlock;
 
-	if (unlikely(rht_grow_above_100(ht, tbl)))
+	if (unlikely(rht_grow_above_100(ht, tbl)) &&
+	    !params->insecure_elasticity)
 		goto slow_path;
 
 	/* Inserting at head of list makes unlocking free. */
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 6074ed5f66f3..b60d55e5b19b 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -538,7 +538,7 @@ static void *rhashtable_lookup_one(struct rhashtable *ht,
 		return NULL;
 	}
 
-	if (elasticity <= 0)
+	if (elasticity <= 0 && !ht->p->insecure_elasticity)
 		return ERR_PTR(-EAGAIN);
 
 	return ERR_PTR(-ENOENT);
@@ -568,7 +568,8 @@ static struct bucket_table *rhashtable_insert_one(
 	if (unlikely(rht_grow_above_max(ht, tbl)))
 		return ERR_PTR(-E2BIG);
 
-	if (unlikely(rht_grow_above_100(ht, tbl)))
+	if (unlikely(rht_grow_above_100(ht, tbl)) &&
+	    !ht->p->insecure_elasticity)
 		return ERR_PTR(-EAGAIN);
 
 	head = rht_ptr(bkt, tbl, hash);
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt