rhashtable: Add rhashtable_free_and_destroy()

rhashtable_destroy() variant which stops rehashes, iterates over
the table and calls a callback to release resources.

Avoids need for nft_hash to embed rhashtable internals and allows to
get rid of the being_destroyed flag. It also saves a 2nd mutex
lock upon destruction.

Also fixes an RCU lockdep splash on nft set destruction due to
calling rht_for_each_entry_safe() without holding bucket locks.
Open code this loop as we need know that no mutations may occur in
parallel.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index ae26c494e2302f9d3c3fe6b04be713d2d53e2a16..99f2e49a8a07889b7e4ef0321c779dfaba7c9b13 100644 (file)
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -136,12 +136,10 @@ struct rhashtable_params {
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
  * @lock: Spin lock to protect walker list
- * @being_destroyed: True if table is set up for destruction
  */
 struct rhashtable {
        struct bucket_table __rcu       *tbl;
        atomic_t                        nelems;
-       bool                            being_destroyed;
        unsigned int                    key_len;
        unsigned int                    elasticity;
        struct rhashtable_params        p;
@@ -334,6 +332,9 @@ int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
 void *rhashtable_walk_next(struct rhashtable_iter *iter);
 void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);
 
+void rhashtable_free_and_destroy(struct rhashtable *ht,
+                                void (*free_fn)(void *ptr, void *arg),
+                                void *arg);
 void rhashtable_destroy(struct rhashtable *ht);
 
 #define rht_dereference(p, ht) \

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 50374d181148ed2979f551097ae0953dd02e75c4..4b7b7e672b934842e9252726d9d1fef6b75f0214 100644 (file)
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -359,8 +359,6 @@ static void rht_deferred_worker(struct work_struct *work)
 
        ht = container_of(work, struct rhashtable, run_work);
        mutex_lock(&ht->mutex);
-       if (ht->being_destroyed)
-               goto unlock;
 
        tbl = rht_dereference(ht->tbl, ht);
        tbl = rhashtable_last_table(ht, tbl);
@@ -372,7 +370,6 @@ static void rht_deferred_worker(struct work_struct *work)
 
        err = rhashtable_rehash_table(ht);
 
-unlock:
        mutex_unlock(&ht->mutex);
 
        if (err)
@@ -783,21 +780,53 @@ int rhashtable_init(struct rhashtable *ht,
 EXPORT_SYMBOL_GPL(rhashtable_init);
 
 /**
- * rhashtable_destroy - destroy hash table
+ * rhashtable_free_and_destroy - free elements and destroy hash table
  * @ht:                the hash table to destroy
+ * @free_fn:   callback to release resources of element
+ * @arg:       pointer passed to free_fn
  *
- * Frees the bucket array. This function is not rcu safe, therefore the caller
- * has to make sure that no resizing may happen by unpublishing the hashtable
- * and waiting for the quiescent cycle before releasing the bucket array.
+ * Stops an eventual async resize. If defined, invokes free_fn for each
+ * element to releasal resources. Please note that RCU protected
+ * readers may still be accessing the elements. Releasing of resources
+ * must occur in a compatible manner. Then frees the bucket array.
+ *
+ * This function will eventually sleep to wait for an async resize
+ * to complete. The caller is responsible that no further write operations
+ * occurs in parallel.
  */
-void rhashtable_destroy(struct rhashtable *ht)
+void rhashtable_free_and_destroy(struct rhashtable *ht,
+                                void (*free_fn)(void *ptr, void *arg),
+                                void *arg)
 {
-       ht->being_destroyed = true;
+       const struct bucket_table *tbl;
+       unsigned int i;
 
        cancel_work_sync(&ht->run_work);
 
        mutex_lock(&ht->mutex);
-       bucket_table_free(rht_dereference(ht->tbl, ht));
+       tbl = rht_dereference(ht->tbl, ht);
+       if (free_fn) {
+               for (i = 0; i < tbl->size; i++) {
+                       struct rhash_head *pos, *next;
+
+                       for (pos = rht_dereference(tbl->buckets[i], ht),
+                            next = !rht_is_a_nulls(pos) ?
+                                       rht_dereference(pos->next, ht) : NULL;
+                            !rht_is_a_nulls(pos);
+                            pos = next,
+                            next = !rht_is_a_nulls(pos) ?
+                                       rht_dereference(pos->next, ht) : NULL)
+                               free_fn(rht_obj(ht, pos), arg);
+               }
+       }
+
+       bucket_table_free(tbl);
        mutex_unlock(&ht->mutex);
 }
+EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
+
+void rhashtable_destroy(struct rhashtable *ht)
+{
+       return rhashtable_free_and_destroy(ht, NULL, NULL);
+}
 EXPORT_SYMBOL_GPL(rhashtable_destroy);

diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
index 8577a37af18b214a668e111e55a6360a709e4d37..f9ce2195fd63e30e725fd96088e55cd2d8743160 100644 (file)
--- a/net/netfilter/nft_hash.c
+++ b/net/netfilter/nft_hash.c
@@ -188,26 +188,15 @@ static int nft_hash_init(const struct nft_set *set,
        return rhashtable_init(priv, &params);
 }
 
-static void nft_hash_destroy(const struct nft_set *set)
+static void nft_free_element(void *ptr, void *arg)
 {
-       struct rhashtable *priv = nft_set_priv(set);
-       const struct bucket_table *tbl;
-       struct nft_hash_elem *he;
-       struct rhash_head *pos, *next;
-       unsigned int i;
-
-       /* Stop an eventual async resizing */
-       priv->being_destroyed = true;
-       mutex_lock(&priv->mutex);
-
-       tbl = rht_dereference(priv->tbl, priv);
-       for (i = 0; i < tbl->size; i++) {
-               rht_for_each_entry_safe(he, pos, next, tbl, i, node)
-                       nft_hash_elem_destroy(set, he);
-       }
-       mutex_unlock(&priv->mutex);
+       nft_hash_elem_destroy((const struct nft_set *)arg, ptr);
+}
 
-       rhashtable_destroy(priv);
+static void nft_hash_destroy(const struct nft_set *set)
+{
+       rhashtable_free_and_destroy(nft_set_priv(set), nft_free_element,
+                                   (void *)set);
 }
 
 static bool nft_hash_estimate(const struct nft_set_desc *desc, u32 features,