Merge branch 'rhashtable-allocation-failure-during-insertion'

Herbert Xu says:

====================
rhashtable: Handle table allocation failure during insertion

v2 -

Added Ack to patch 2.
Fixed RCU annotation in code path executed by rehasher by using
rht_dereference_bucket.

v1 -

This series tackles the problem of table allocation failures during
insertion.  The issue is that we cannot vmalloc during insertion.
This series deals with this by introducing nested tables.

The first two patches removes manual hash table walks which cannot
work on a nested table.

The final patch introduces nested tables.

I've tested this with test_rhashtable and it appears to work.
====================

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

fs/gfs2/glock.c

@@ -1420,26 +1420,32 @@ static struct shrinker glock_shrinker = {
  * @sdp: the filesystem
  * @bucket: the bucket
  *
+ * Note that the function can be called multiple times on the same
+ * object.  So the user must ensure that the function can cope with
+ * that.
  */
 
 static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
 {
 	struct gfs2_glock *gl;
-	struct rhash_head *pos;
-	const struct bucket_table *tbl;
-	int i;
+	struct rhashtable_iter iter;
 
-	rcu_read_lock();
-	tbl = rht_dereference_rcu(gl_hash_table.tbl, &gl_hash_table);
-	for (i = 0; i < tbl->size; i++) {
-		rht_for_each_entry_rcu(gl, pos, tbl, i, gl_node) {
+	rhashtable_walk_enter(&gl_hash_table, &iter);
+
+	do {
+		gl = ERR_PTR(rhashtable_walk_start(&iter));
+		if (gl)
+			continue;
+
+		while ((gl = rhashtable_walk_next(&iter)) && !IS_ERR(gl))
 			if ((gl->gl_name.ln_sbd == sdp) &&
 			    lockref_get_not_dead(&gl->gl_lockref))
 				examiner(gl);
-		}
-	}
-	rcu_read_unlock();
-	cond_resched();
+
+		rhashtable_walk_stop(&iter);
+	} while (cond_resched(), gl == ERR_PTR(-EAGAIN));
+
+	rhashtable_walk_exit(&iter);
 }
 
 /**

include/linux/rhashtable.h

@@ -61,17 +61,20 @@ struct rhlist_head {
 /**
  * struct bucket_table - Table of hash buckets
  * @size: Number of hash buckets
+ * @nest: Number of bits of first-level nested table.
  * @rehash: Current bucket being rehashed
  * @hash_rnd: Random seed to fold into hash
  * @locks_mask: Mask to apply before accessing locks[]
  * @locks: Array of spinlocks protecting individual buckets
  * @walkers: List of active walkers
  * @rcu: RCU structure for freeing the table
  * @future_tbl: Table under construction during rehashing
+ * @ntbl: Nested table used when out of memory.
  * @buckets: size * hash buckets
  */
 struct bucket_table {
 	unsigned int		size;
+	unsigned int		nest;
 	unsigned int		rehash;
 	u32			hash_rnd;
 	unsigned int		locks_mask;
@@ -81,7 +84,7 @@ struct bucket_table {
 
 	struct bucket_table __rcu *future_tbl;
 
-	struct rhash_head __rcu	*buckets[] ____cacheline_aligned_in_smp;
+	struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
 };
 
 /**
@@ -374,6 +377,12 @@ void rhashtable_free_and_destroy(struct rhashtable *ht,
 				 void *arg);
 void rhashtable_destroy(struct rhashtable *ht);
 
+struct rhash_head __rcu **rht_bucket_nested(const struct bucket_table *tbl,
+					    unsigned int hash);
+struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
+						   struct bucket_table *tbl,
+						   unsigned int hash);
+
 #define rht_dereference(p, ht) \
 	rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
 
@@ -389,6 +398,27 @@ void rhashtable_destroy(struct rhashtable *ht);
 #define rht_entry(tpos, pos, member) \
 	({ tpos = container_of(pos, typeof(*tpos), member); 1; })
 
+static inline struct rhash_head __rcu *const *rht_bucket(
+	const struct bucket_table *tbl, unsigned int hash)
+{
+	return unlikely(tbl->nest) ? rht_bucket_nested(tbl, hash) :
+				     &tbl->buckets[hash];
+}
+
+static inline struct rhash_head __rcu **rht_bucket_var(
+	struct bucket_table *tbl, unsigned int hash)
+{
+	return unlikely(tbl->nest) ? rht_bucket_nested(tbl, hash) :
+				     &tbl->buckets[hash];
+}
+
+static inline struct rhash_head __rcu **rht_bucket_insert(
+	struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash)
+{
+	return unlikely(tbl->nest) ? rht_bucket_nested_insert(ht, tbl, hash) :
+				     &tbl->buckets[hash];
+}
+
 /**
  * rht_for_each_continue - continue iterating over hash chain
  * @pos:	the &struct rhash_head to use as a loop cursor.
@@ -408,7 +438,7 @@ void rhashtable_destroy(struct rhashtable *ht);
  * @hash:	the hash value / bucket index
  */
 #define rht_for_each(pos, tbl, hash) \
-	rht_for_each_continue(pos, (tbl)->buckets[hash], tbl, hash)
+	rht_for_each_continue(pos, *rht_bucket(tbl, hash), tbl, hash)
 
 /**
  * rht_for_each_entry_continue - continue iterating over hash chain
@@ -433,7 +463,7 @@ void rhashtable_destroy(struct rhashtable *ht);
  * @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, (tbl)->buckets[hash],	\
+	rht_for_each_entry_continue(tpos, pos, *rht_bucket(tbl, hash),	\
 				    tbl, hash, member)
 
 /**
@@ -448,13 +478,13 @@ void rhashtable_destroy(struct rhashtable *ht);
  * This hash chain list-traversal primitive allows for the looped code to
  * remove the loop cursor from the list.
  */
-#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member)	    \
-	for (pos = rht_dereference_bucket((tbl)->buckets[hash], tbl, hash), \
-	     next = !rht_is_a_nulls(pos) ?				    \
-		       rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
-	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	    \
-	     pos = next,						    \
-	     next = !rht_is_a_nulls(pos) ?				    \
+#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member)	      \
+	for (pos = rht_dereference_bucket(*rht_bucket(tbl, hash), tbl, hash), \
+	     next = !rht_is_a_nulls(pos) ?				      \
+		       rht_dereference_bucket(pos->next, tbl, hash) : NULL;   \
+	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	      \
+	     pos = next,						      \
+	     next = !rht_is_a_nulls(pos) ?				      \
 		       rht_dereference_bucket(pos->next, tbl, hash) : NULL)
 
 /**
@@ -485,7 +515,7 @@ void rhashtable_destroy(struct rhashtable *ht);
  * traversal is guarded by rcu_read_lock().
  */
 #define rht_for_each_rcu(pos, tbl, hash)				\
-	rht_for_each_rcu_continue(pos, (tbl)->buckets[hash], tbl, hash)
+	rht_for_each_rcu_continue(pos, *rht_bucket(tbl, hash), tbl, hash)
 
 /**
  * rht_for_each_entry_rcu_continue - continue iterating over rcu hash chain
@@ -518,8 +548,8 @@ void rhashtable_destroy(struct rhashtable *ht);
  * 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(tpos, pos, tbl, hash, member)		\
-	rht_for_each_entry_rcu_continue(tpos, pos, (tbl)->buckets[hash],\
+#define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member)		   \
+	rht_for_each_entry_rcu_continue(tpos, pos, *rht_bucket(tbl, hash), \
 					tbl, hash, member)
 
 /**
@@ -565,7 +595,7 @@ static inline struct rhash_head *__rhashtable_lookup(
 		.ht = ht,
 		.key = key,
 	};
-	const struct bucket_table *tbl;
+	struct bucket_table *tbl;
 	struct rhash_head *he;
 	unsigned int hash;
 
@@ -697,8 +727,12 @@ static inline void *__rhashtable_insert_fast(
 	}
 
 	elasticity = ht->elasticity;
-	pprev = &tbl->buckets[hash];
-	rht_for_each(head, tbl, hash) {
+	pprev = rht_bucket_insert(ht, tbl, hash);
+	data = ERR_PTR(-ENOMEM);
+	if (!pprev)
+		goto out;
+
+	rht_for_each_continue(head, *pprev, tbl, hash) {
 		struct rhlist_head *plist;
 		struct rhlist_head *list;
 
@@ -736,7 +770,7 @@ static inline void *__rhashtable_insert_fast(
 	if (unlikely(rht_grow_above_100(ht, tbl)))
 		goto slow_path;
 
-	head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
+	head = rht_dereference_bucket(*pprev, tbl, hash);
 
 	RCU_INIT_POINTER(obj->next, head);
 	if (rhlist) {
@@ -746,7 +780,7 @@ static inline void *__rhashtable_insert_fast(
 		RCU_INIT_POINTER(list->next, NULL);
 	}
 
-	rcu_assign_pointer(tbl->buckets[hash], obj);
+	rcu_assign_pointer(*pprev, obj);
 
 	atomic_inc(&ht->nelems);
 	if (rht_grow_above_75(ht, tbl))
@@ -955,8 +989,8 @@ static inline int __rhashtable_remove_fast_one(
 
 	spin_lock_bh(lock);
 
-	pprev = &tbl->buckets[hash];
-	rht_for_each(he, tbl, hash) {
+	pprev = rht_bucket_var(tbl, hash);
+	rht_for_each_continue(he, *pprev, tbl, hash) {
 		struct rhlist_head *list;
 
 		list = container_of(he, struct rhlist_head, rhead);
@@ -1107,8 +1141,8 @@ static inline int __rhashtable_replace_fast(
 
 	spin_lock_bh(lock);
 
-	pprev = &tbl->buckets[hash];
-	rht_for_each(he, tbl, hash) {
+	pprev = rht_bucket_var(tbl, hash);
+	rht_for_each_continue(he, *pprev, tbl, hash) {
 		if (he != obj_old) {
 			pprev = &he->next;
 			continue;