Merge branch 'rhashtable-next'

Herbert Xu says:

====================
rhashtable: Add iterators and use them

The first patch fixes a potential crash with nft_hash destroying
the table during a shrinking process.  While the next patch adds
rhashtable iterators to replace current manual walks used by
netlink and netfilter.  The final two patches make use of these
iterators in netlink and netfilter.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 302 insertions, 83 deletions

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index e0337844358e..58851275fed9 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -18,6 +18,7 @@
 #ifndef _LINUX_RHASHTABLE_H
 #define _LINUX_RHASHTABLE_H
 
+#include <linux/compiler.h>
 #include <linux/list_nulls.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
@@ -111,6 +112,7 @@ struct rhashtable_params {
  * @p: Configuration parameters
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
+ * @walkers: List of active walkers
  * @being_destroyed: True if table is set up for destruction
  */
 struct rhashtable {
@@ -121,9 +123,36 @@ struct rhashtable {
         struct rhashtable_params        p;
         struct work_struct              run_work;
         struct mutex                    mutex;
+        struct list_head                walkers;
         bool                            being_destroyed;
 };
 
+/**
+ * struct rhashtable_walker - Hash table walker
+ * @list: List entry on list of walkers
+ * @resize: Resize event occured
+ */
+struct rhashtable_walker {
+        struct list_head list;
+        bool resize;
+};
+
+/**
+ * struct rhashtable_iter - Hash table iterator, fits into netlink cb
+ * @ht: Table to iterate through
+ * @p: Current pointer
+ * @walker: Associated rhashtable walker
+ * @slot: Current slot
+ * @skip: Number of entries to skip in slot
+ */
+struct rhashtable_iter {
+        struct rhashtable *ht;
+        struct rhash_head *p;
+        struct rhashtable_walker *walker;
+        unsigned int slot;
+        unsigned int skip;
+};
+
 static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)
 {
         return NULLS_MARKER(ht->p.nulls_base + hash);
@@ -179,6 +208,12 @@ bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
                                       bool (*compare)(void *, void *),
                                       void *arg);
 
+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);
+void *rhashtable_walk_next(struct rhashtable_iter *iter);
+void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);
+
 void rhashtable_destroy(struct rhashtable *ht);
 
 #define rht_dereference(p, ht) \
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index c41e21096373..057919164e23 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -484,16 +484,24 @@ static void rht_deferred_worker(struct work_struct *work)
 {
         struct rhashtable *ht;
         struct bucket_table *tbl;
+        struct rhashtable_walker *walker;
 
         ht = container_of(work, struct rhashtable, run_work);
         mutex_lock(&ht->mutex);
+        if (ht->being_destroyed)
+                goto unlock;
+
         tbl = rht_dereference(ht->tbl, ht);
 
+        list_for_each_entry(walker, &ht->walkers, list)
+                walker->resize = true;
+
         if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
                 rhashtable_expand(ht);
         else if (ht->p.shrink_decision && ht->p.shrink_decision(ht, tbl->size))
                 rhashtable_shrink(ht);
 
+unlock:
         mutex_unlock(&ht->mutex);
 }
 
@@ -818,6 +826,164 @@ exit:
 }
 EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);
 
+/**
+ * rhashtable_walk_init - Initialise an iterator
+ * @ht:         Table to walk over
+ * @iter:       Hash table Iterator
+ *
+ * This function prepares a hash table walk.
+ *
+ * Note that if you restart a walk after rhashtable_walk_stop you
+ * may see the same object twice.  Also, you may miss objects if
+ * there are removals in between rhashtable_walk_stop and the next
+ * call to rhashtable_walk_start.
+ *
+ * For a completely stable walk you should construct your own data
+ * structure outside the hash table.
+ *
+ * This function may sleep so you must not call it from interrupt
+ * context or with spin locks held.
+ *
+ * You must call rhashtable_walk_exit if this function returns
+ * successfully.
+ */
+int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
+{
+        iter->ht = ht;
+        iter->p = NULL;
+        iter->slot = 0;
+        iter->skip = 0;
+
+        iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
+        if (!iter->walker)
+                return -ENOMEM;
+
+        mutex_lock(&ht->mutex);
+        list_add(&iter->walker->list, &ht->walkers);
+        mutex_unlock(&ht->mutex);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_walk_init);
+
+/**
+ * rhashtable_walk_exit - Free an iterator
+ * @iter:       Hash table Iterator
+ *
+ * This function frees resources allocated by rhashtable_walk_init.
+ */
+void rhashtable_walk_exit(struct rhashtable_iter *iter)
+{
+        mutex_lock(&iter->ht->mutex);
+        list_del(&iter->walker->list);
+        mutex_unlock(&iter->ht->mutex);
+        kfree(iter->walker);
+}
+EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
+
+/**
+ * rhashtable_walk_start - Start a hash table walk
+ * @iter:       Hash table iterator
+ *
+ * Start a hash table walk.  Note that we take the RCU lock in all
+ * cases including when we return an error.  So you must always call
+ * rhashtable_walk_stop to clean up.
+ *
+ * Returns zero if successful.
+ *
+ * Returns -EAGAIN if resize event occured.  Note that the iterator
+ * will rewind back to the beginning and you may use it immediately
+ * by calling rhashtable_walk_next.
+ */
+int rhashtable_walk_start(struct rhashtable_iter *iter)
+{
+        rcu_read_lock();
+
+        if (iter->walker->resize) {
+                iter->slot = 0;
+                iter->skip = 0;
+                iter->walker->resize = false;