1 files changed, 93 insertions, 7 deletions

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 843ceca9a21e..63bd7601b6de 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -19,6 +19,7 @@
 
 #include <linux/atomic.h>
 #include <linux/compiler.h>
+#include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/jhash.h>
 #include <linux/list_nulls.h>
@@ -339,10 +340,11 @@ static inline int lockdep_rht_bucket_is_held(const struct bucket_table *tbl,
 int rhashtable_init(struct rhashtable *ht,
 		    const struct rhashtable_params *params);
 
-int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
-			   struct rhash_head *obj,
-			   struct bucket_table *old_tbl);
-int rhashtable_insert_rehash(struct rhashtable *ht);
+struct bucket_table *rhashtable_insert_slow(struct rhashtable *ht,
+					    const void *key,
+					    struct rhash_head *obj,
+					    struct bucket_table *old_tbl);
+int rhashtable_insert_rehash(struct rhashtable *ht, struct bucket_table *tbl);
 
 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter);
 void rhashtable_walk_exit(struct rhashtable_iter *iter);
@@ -598,9 +600,11 @@ restart:
 
 	new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 	if (unlikely(new_tbl)) {
-		err = rhashtable_insert_slow(ht, key, obj, new_tbl);
-		if (err == -EAGAIN)
+		tbl = rhashtable_insert_slow(ht, key, obj, new_tbl);
+		if (!IS_ERR_OR_NULL(tbl))
 			goto slow_path;
+
+		err = PTR_ERR(tbl);
 		goto out;
 	}
 
@@ -611,7 +615,7 @@ restart:
 	if (unlikely(rht_grow_above_100(ht, tbl))) {
 slow_path:
 		spin_unlock_bh(lock);
-		err = rhashtable_insert_rehash(ht);
+		err = rhashtable_insert_rehash(ht, tbl);
 		rcu_read_unlock();
 		if (err)
 			return err;
@@ -819,4 +823,86 @@ out:
 	return err;
 }
 
+/* Internal function, please use rhashtable_replace_fast() instead */
+static inline int __rhashtable_replace_fast(
+	struct rhashtable *ht, struct bucket_table *tbl,
+	struct rhash_head *obj_old, struct rhash_head *obj_new,
+	const struct rhashtable_params params)
+{
+	struct rhash_head __rcu **pprev;
+	struct rhash_head *he;
+	spinlock_t *lock;
+	unsigned int hash;
+	int err = -ENOENT;
+
+	/* Minimally, the old and new objects must have same hash
+	 * (which should mean identifiers are the same).
+	 */
+	hash = rht_head_hashfn(ht, tbl, obj_old, params);
+	if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
+		return -EINVAL;
+
+	lock = rht_bucket_lock(tbl, hash);
+
+	spin_lock_bh(lock);
+
+	pprev = &tbl->buckets[hash];
+	rht_for_each(he, tbl, hash) {
+		if (he != obj_old) {
+			pprev = &he->next;
+			continue;
+		}
+
+		rcu_assign_pointer(obj_new->next, obj_old->next);
+		rcu_assign_pointer(*pprev, obj_new);
+		err = 0;
+		break;
+	}
+
+	spin_unlock_bh(lock);
+
+	return err;
+}
+
+/**
+ * rhashtable_replace_fast - replace an object in hash table
+ * @ht:		hash table
+ * @obj_old:	pointer to hash head inside object being replaced
+ * @obj_new:	pointer to hash head inside object which is new
+ * @params:	hash table parameters
+ *
+ * Replacing an object doesn't affect the number of elements in the hash table
+ * or bucket, so we don't need to worry about shrinking or expanding the
+ * table here.
+ *
+ * Returns zero on success, -ENOENT if the entry could not be found,
+ * -EINVAL if hash is not the same for the old and new objects.
+ */
+static inline int rhashtable_replace_fast(
+	struct rhashtable *ht, struct rhash_head *obj_old,
+	struct rhash_head *obj_new,
+	const struct rhashtable_params params)
+{
+	struct bucket_table *tbl;
+	int err;
+
+	rcu_read_lock();
+
+	tbl = rht_dereference_rcu(ht->tbl, ht);
+
+	/* Because we have already taken (and released) the bucket
+	 * lock in old_tbl, if we find that future_tbl is not yet
+	 * visible then that guarantees the entry to still be in
+	 * the old tbl if it exists.
+	 */
+	while ((err = __rhashtable_replace_fast(ht, tbl, obj_old,
+						obj_new, params)) &&
+	       (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
+		;
+
+	rcu_read_unlock();
+
+	return err;
+}
+
 #endif /* _LINUX_RHASHTABLE_H */