Merge branch 'rhashtable-cleanups'

NeilBrown says:

====================
Two clean-ups for rhashtable.

These two patches make small improvements to
rhashtable, but are otherwise unrelated.

Thanks to Herbert, Miguel, and Paul for the review.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

.clang-format

@@ -366,14 +366,14 @@ ForEachMacros:
   - 'rhl_for_each_entry_rcu'
   - 'rhl_for_each_rcu'
   - 'rht_for_each'
-  - 'rht_for_each_continue'
+  - 'rht_for_each_from'
   - 'rht_for_each_entry'
-  - 'rht_for_each_entry_continue'
+  - 'rht_for_each_entry_from'
   - 'rht_for_each_entry_rcu'
-  - 'rht_for_each_entry_rcu_continue'
+  - 'rht_for_each_entry_rcu_from'
   - 'rht_for_each_entry_safe'
   - 'rht_for_each_rcu'
-  - 'rht_for_each_rcu_continue'
+  - 'rht_for_each_rcu_from'
   - '__rq_for_each_bio'
   - 'rq_for_each_segment'
   - 'scsi_for_each_prot_sg'

include/linux/rhashtable.h

@@ -63,7 +63,6 @@
 struct bucket_table {
 	unsigned int		size;
 	unsigned int		nest;
-	unsigned int		rehash;
 	u32			hash_rnd;
 	unsigned int		locks_mask;
 	spinlock_t		*locks;
@@ -307,13 +306,13 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
 }
 
 /**
- * rht_for_each_continue - continue iterating over hash chain
+ * rht_for_each_from - iterate over hash chain from given head
  * @pos:	the &struct rhash_head to use as a loop cursor.
- * @head:	the previous &struct rhash_head to continue from
+ * @head:	the &struct rhash_head to start from
  * @tbl:	the &struct bucket_table
  * @hash:	the hash value / bucket index
  */
-#define rht_for_each_continue(pos, head, tbl, hash) \
+#define rht_for_each_from(pos, head, tbl, hash) \
 	for (pos = rht_dereference_bucket(head, tbl, hash); \
 	     !rht_is_a_nulls(pos); \
 	     pos = rht_dereference_bucket((pos)->next, tbl, hash))
@@ -325,18 +324,18 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * @hash:	the hash value / bucket index
  */
 #define rht_for_each(pos, tbl, hash) \
-	rht_for_each_continue(pos, *rht_bucket(tbl, hash), tbl, hash)
+	rht_for_each_from(pos, *rht_bucket(tbl, hash), tbl, hash)
 
 /**
- * rht_for_each_entry_continue - continue iterating over hash chain
+ * rht_for_each_entry_from - iterate over hash chain from given head
  * @tpos:	the type * to use as a loop cursor.
  * @pos:	the &struct rhash_head to use as a loop cursor.
- * @head:	the previous &struct rhash_head to continue from
+ * @head:	the &struct rhash_head to start from
  * @tbl:	the &struct bucket_table
  * @hash:	the hash value / bucket index
  * @member:	name of the &struct rhash_head within the hashable struct.
  */
-#define rht_for_each_entry_continue(tpos, pos, head, tbl, hash, member)	\
+#define rht_for_each_entry_from(tpos, pos, head, tbl, hash, member)	\
 	for (pos = rht_dereference_bucket(head, tbl, hash);		\
 	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	\
 	     pos = rht_dereference_bucket((pos)->next, tbl, hash))
@@ -350,7 +349,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * @member:	name of the &struct rhash_head within the hashable struct.
  */
 #define rht_for_each_entry(tpos, pos, tbl, hash, member)		\
-	rht_for_each_entry_continue(tpos, pos, *rht_bucket(tbl, hash),	\
+	rht_for_each_entry_from(tpos, pos, *rht_bucket(tbl, hash),	\
 				    tbl, hash, member)
 
 /**
@@ -375,9 +374,9 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
 		       rht_dereference_bucket(pos->next, tbl, hash) : NULL)
 
 /**
- * rht_for_each_rcu_continue - continue iterating over rcu hash chain
+ * rht_for_each_rcu_from - iterate over rcu hash chain from given head
  * @pos:	the &struct rhash_head to use as a loop cursor.
- * @head:	the previous &struct rhash_head to continue from
+ * @head:	the &struct rhash_head to start from
  * @tbl:	the &struct bucket_table
  * @hash:	the hash value / bucket index
  *
@@ -385,7 +384,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * the _rcu mutation primitives such as rhashtable_insert() as long as the
  * traversal is guarded by rcu_read_lock().
  */
-#define rht_for_each_rcu_continue(pos, head, tbl, hash)			\
+#define rht_for_each_rcu_from(pos, head, tbl, hash)			\
 	for (({barrier(); }),						\
 	     pos = rht_dereference_bucket_rcu(head, tbl, hash);		\
 	     !rht_is_a_nulls(pos);					\
@@ -402,13 +401,13 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * traversal is guarded by rcu_read_lock().
  */
 #define rht_for_each_rcu(pos, tbl, hash)				\
-	rht_for_each_rcu_continue(pos, *rht_bucket(tbl, hash), tbl, hash)
+	rht_for_each_rcu_from(pos, *rht_bucket(tbl, hash), tbl, hash)
 
 /**
- * rht_for_each_entry_rcu_continue - continue iterating over rcu hash chain
+ * rht_for_each_entry_rcu_from - iterated over rcu hash chain from given head
  * @tpos:	the type * to use as a loop cursor.
  * @pos:	the &struct rhash_head to use as a loop cursor.
- * @head:	the previous &struct rhash_head to continue from
+ * @head:	the &struct rhash_head to start from
  * @tbl:	the &struct bucket_table
  * @hash:	the hash value / bucket index
  * @member:	name of the &struct rhash_head within the hashable struct.
@@ -417,7 +416,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * the _rcu mutation primitives such as rhashtable_insert() as long as the
  * traversal is guarded by rcu_read_lock().
  */
-#define rht_for_each_entry_rcu_continue(tpos, pos, head, tbl, hash, member) \
+#define rht_for_each_entry_rcu_from(tpos, pos, head, tbl, hash, member) \
 	for (({barrier(); }),						    \
 	     pos = rht_dereference_bucket_rcu(head, tbl, hash);		    \
 	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	    \
@@ -436,7 +435,7 @@ static inline struct rhash_head __rcu **rht_bucket_insert(
  * traversal is guarded by rcu_read_lock().
  */
 #define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member)		   \
-	rht_for_each_entry_rcu_continue(tpos, pos, *rht_bucket(tbl, hash), \
+	rht_for_each_entry_rcu_from(tpos, pos, *rht_bucket(tbl, hash), \
 					tbl, hash, member)
 
 /**
@@ -492,7 +491,7 @@ static inline struct rhash_head *__rhashtable_lookup(
 	hash = rht_key_hashfn(ht, tbl, key, params);
 	head = rht_bucket(tbl, hash);
 	do {
-		rht_for_each_rcu_continue(he, *head, tbl, hash) {
+		rht_for_each_rcu_from(he, *head, tbl, hash) {
 			if (params.obj_cmpfn ?
 			    params.obj_cmpfn(&arg, rht_obj(ht, he)) :
 			    rhashtable_compare(&arg, rht_obj(ht, he)))
@@ -626,7 +625,7 @@ static inline void *__rhashtable_insert_fast(
 	if (!pprev)
 		goto out;
 
-	rht_for_each_continue(head, *pprev, tbl, hash) {
+	rht_for_each_from(head, *pprev, tbl, hash) {
 		struct rhlist_head *plist;
 		struct rhlist_head *list;
 
@@ -776,12 +775,6 @@ static inline int rhltable_insert(
  * @obj:	pointer to hash head inside object
  * @params:	hash table parameters
  *
- * Locks down the bucket chain in both the old and new table if a resize
- * is in progress to ensure that writers can't remove from the old table
- * and can't insert to the new table during the atomic operation of search
- * and insertion. Searches for duplicates in both the old and new table if
- * a resize is in progress.
- *
  * This lookup function may only be used for fixed key hash table (key_len
  * parameter set). It will BUG() if used inappropriately.
  *
@@ -837,12 +830,6 @@ static inline void *rhashtable_lookup_get_insert_fast(
  * @obj:	pointer to hash head inside object
  * @params:	hash table parameters
  *
- * Locks down the bucket chain in both the old and new table if a resize
- * is in progress to ensure that writers can't remove from the old table
- * and can't insert to the new table during the atomic operation of search
- * and insertion. Searches for duplicates in both the old and new table if
- * a resize is in progress.
- *
  * Lookups may occur in parallel with hashtable mutations and resizing.
  *
  * Will trigger an automatic deferred table resizing if residency in the
@@ -903,7 +890,7 @@ static inline int __rhashtable_remove_fast_one(
 	spin_lock_bh(lock);
 
 	pprev = rht_bucket_var(tbl, hash);
-	rht_for_each_continue(he, *pprev, tbl, hash) {
+	rht_for_each_from(he, *pprev, tbl, hash) {
 		struct rhlist_head *list;
 
 		list = container_of(he, struct rhlist_head, rhead);
@@ -1055,7 +1042,7 @@ static inline int __rhashtable_replace_fast(
 	spin_lock_bh(lock);
 
 	pprev = rht_bucket_var(tbl, hash);
-	rht_for_each_continue(he, *pprev, tbl, hash) {
+	rht_for_each_from(he, *pprev, tbl, hash) {
 		if (he != obj_old) {
 			pprev = &he->next;
 			continue;

lib/rhashtable.c

@@ -197,6 +197,7 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 		return NULL;
 	}
 
+	rcu_head_init(&tbl->rcu);
 	INIT_LIST_HEAD(&tbl->walkers);
 
 	tbl->hash_rnd = get_random_u32();
@@ -280,10 +281,9 @@ static int rhashtable_rehash_chain(struct rhashtable *ht,
 	while (!(err = rhashtable_rehash_one(ht, old_hash)))
 		;
 
-	if (err == -ENOENT) {
-		old_tbl->rehash++;
+	if (err == -ENOENT)
 		err = 0;
-	}
+
 	spin_unlock_bh(old_bucket_lock);
 
 	return err;
@@ -330,13 +330,16 @@ static int rhashtable_rehash_table(struct rhashtable *ht)
 	spin_lock(&ht->lock);
 	list_for_each_entry(walker, &old_tbl->walkers, list)
 		walker->tbl = NULL;
-	spin_unlock(&ht->lock);
 
 	/* Wait for readers. All new readers will see the new
 	 * table, and thus no references to the old table will
 	 * remain.
+	 * We do this inside the locked region so that
+	 * rhashtable_walk_stop() can use rcu_head_after_call_rcu()
+	 * to check if it should not re-link the table.
 	 */
 	call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
+	spin_unlock(&ht->lock);
 
 	return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 }
@@ -487,7 +490,7 @@ static void *rhashtable_lookup_one(struct rhashtable *ht,
 
 	elasticity = RHT_ELASTICITY;
 	pprev = rht_bucket_var(tbl, hash);
-	rht_for_each_continue(head, *pprev, tbl, hash) {
+	rht_for_each_from(head, *pprev, tbl, hash) {
 		struct rhlist_head *list;
 		struct rhlist_head *plist;
 
@@ -578,46 +581,22 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
 	struct bucket_table *new_tbl;
 	struct bucket_table *tbl;
 	unsigned int hash;
-	spinlock_t *lock;
 	void *data;
 
-	tbl = rcu_dereference(ht->tbl);
-
-	/* All insertions must grab the oldest table containing
-	 * the hashed bucket that is yet to be rehashed.
-	 */
-	for (;;) {
-		hash = rht_head_hashfn(ht, tbl, obj, ht->p);
-		lock = rht_bucket_lock(tbl, hash);
-		spin_lock_bh(lock);
-
-		if (tbl->rehash <= hash)
-			break;
-
-		spin_unlock_bh(lock);
-		tbl = rht_dereference_rcu(tbl->future_tbl, ht);
-	}
-
-	data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
-	new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
-	if (PTR_ERR(new_tbl) != -EEXIST)
-		data = ERR_CAST(new_tbl);
+	new_tbl = rcu_dereference(ht->tbl);
 
-	while (!IS_ERR_OR_NULL(new_tbl)) {
+	do {
 		tbl = new_tbl;
 		hash = rht_head_hashfn(ht, tbl, obj, ht->p);
-		spin_lock_nested(rht_bucket_lock(tbl, hash),
-				 SINGLE_DEPTH_NESTING);
+		spin_lock_bh(rht_bucket_lock(tbl, hash));
 
 		data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
 		new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
 		if (PTR_ERR(new_tbl) != -EEXIST)
 			data = ERR_CAST(new_tbl);
 
-		spin_unlock(rht_bucket_lock(tbl, hash));
-	}
-
-	spin_unlock_bh(lock);
+		spin_unlock_bh(rht_bucket_lock(tbl, hash));
+	} while (!IS_ERR_OR_NULL(new_tbl));
 
 	if (PTR_ERR(data) == -EAGAIN)
 		data = ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?:
@@ -939,10 +918,11 @@ void rhashtable_walk_stop(struct rhashtable_iter *iter)
 	ht = iter->ht;
 
 	spin_lock(&ht->lock);
-	if (tbl->rehash < tbl->size)
-		list_add(&iter->walker.list, &tbl->walkers);
-	else
+	if (rcu_head_after_call_rcu(&tbl->rcu, bucket_table_free_rcu))
+		/* This bucket table is being freed, don't re-link it. */
 		iter->walker.tbl = NULL;
+	else
+		list_add(&iter->walker.list, &tbl->walkers);
 	spin_unlock(&ht->lock);
 
 out: