X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=rcuja%2Frcuja.c;h=34f3191a39037c24a058d33f0ebfabc405c0a82c;hb=b1a90ce30f17800630d578f32a05c2ad5eac0cae;hp=97381437368d295380de5230bc9c72ed9217a9ca;hpb=b306a0fe21a4bde8ce65d35bbf4a836bdb72be68;p=userspace-rcu.git

diff --git a/rcuja/rcuja.c b/rcuja/rcuja.c
index 9738143..34f3191 100644
--- a/rcuja/rcuja.c
+++ b/rcuja/rcuja.c
@@ -24,6 +24,7 @@
 #include <stdint.h>
 #include <errno.h>
 #include <limits.h>
+#include <string.h>
 #include <urcu/rcuja.h>
 #include <urcu/compiler.h>
 #include <urcu/arch.h>
@@ -35,6 +36,10 @@
 #include "rcuja-internal.h"
 #include "bitfield.h"
 
+#ifndef abs
+#define abs_int(a)	((int) (a) > 0 ? (int) (a) : -((int) (a)))
+#endif
+
 enum cds_ja_type_class {
 	RCU_JA_LINEAR = 0,	/* Type A */
 			/* 32-bit: 1 to 25 children, 8 to 128 bytes */
@@ -120,8 +125,8 @@ const struct cds_ja_type ja_types[] = {
 	{ .type_class = RCU_JA_POOL, .min_child = 45, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 9, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 7, },
 
 	/*
-	 * TODO: Upon node removal below min_child, if child pool is
-	 * filled beyond capacity, we need to roll back to pigeon.
+	 * Upon node removal below min_child, if child pool is filled
+	 * beyond capacity, we roll back to pigeon.
 	 */
 	{ .type_class = RCU_JA_PIGEON, .min_child = 89, .max_child = ja_type_7_max_child, .order = 10, },
 
@@ -168,8 +173,8 @@ const struct cds_ja_type ja_types[] = {
 	{ .type_class = RCU_JA_POOL, .min_child = 51, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 10, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 8, },
 
 	/*
-	 * TODO: Upon node removal below min_child, if child pool is
-	 * filled beyond capacity, we need to roll back to pigeon.
+	 * Upon node removal below min_child, if child pool is filled
+	 * beyond capacity, we roll back to pigeon.
 	 */
 	{ .type_class = RCU_JA_PIGEON, .min_child = 101, .max_child = ja_type_7_max_child, .order = 11, },
 
@@ -239,9 +244,60 @@ enum ja_recompact {
 	JA_RECOMPACT_DEL,
 };
 
+static
+struct cds_ja_inode *_ja_node_mask_ptr(struct cds_ja_inode_flag *node)
+{
+	return (struct cds_ja_inode *) (((unsigned long) node) & JA_PTR_MASK);
+}
+
+unsigned long ja_node_type(struct cds_ja_inode_flag *node)
+{
+	unsigned long type;
+
+	if (_ja_node_mask_ptr(node) == NULL) {
+		return NODE_INDEX_NULL;
+	}
+	type = (unsigned int) ((unsigned long) node & JA_TYPE_MASK);
+	assert(type < (1UL << JA_TYPE_BITS));
+	return type;
+}
+
+struct cds_ja_inode *ja_node_ptr(struct cds_ja_inode_flag *node)
+{
+	unsigned long type_index = ja_node_type(node);
+	const struct cds_ja_type *type;
+
+	type = &ja_types[type_index];
+	switch (type->type_class) {
+	case RCU_JA_LINEAR:
+	case RCU_JA_PIGEON:	/* fall-through */
+	case RCU_JA_NULL:	/* fall-through */
+	default:		/* fall-through */
+		return _ja_node_mask_ptr(node);
+	case RCU_JA_POOL:
+		switch (type->nr_pool_order) {
+		case 1:
+			return (struct cds_ja_inode *) (((unsigned long) node) & ~(JA_POOL_1D_MASK | JA_TYPE_MASK));
+		case 2:
+			return (struct cds_ja_inode *) (((unsigned long) node) & ~(JA_POOL_2D_MASK | JA_POOL_1D_MASK | JA_TYPE_MASK));
+		default:
+			assert(0);
+		}
+	}
+}
+
 struct cds_ja_inode *alloc_cds_ja_node(const struct cds_ja_type *ja_type)
 {
-	return calloc(1U << ja_type->order, sizeof(char));
+	size_t len = 1U << ja_type->order;
+	void *p;
+	int ret;
+
+	ret = posix_memalign(&p, len, len);
+	if (ret || !p) {
+		return NULL;
+	}
+	memset(p, 0, len);
+	return p;
 }
 
 void free_cds_ja_node(struct cds_ja_inode *node)
@@ -277,6 +333,8 @@ static
 struct cds_ja_inode_flag *ja_linear_node_get_nth(const struct cds_ja_type *type,
 		struct cds_ja_inode *node,
 		struct cds_ja_inode_flag ***child_node_flag_ptr,
+		struct cds_ja_inode_flag **child_node_flag_v,
+		struct cds_ja_inode_flag ***node_flag_ptr,
 		uint8_t n)
 {
 	uint8_t nr_child;
@@ -297,12 +355,19 @@ struct cds_ja_inode_flag *ja_linear_node_get_nth(const struct cds_ja_type *type,
 		if (CMM_LOAD_SHARED(values[i]) == n)
 			break;
 	}
-	if (i >= nr_child)
+	if (i >= nr_child) {
+		if (caa_unlikely(node_flag_ptr))
+			*node_flag_ptr = NULL;
 		return NULL;
+	}
 	pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
 	ptr = rcu_dereference(pointers[i]);
 	if (caa_unlikely(child_node_flag_ptr) && ptr)
 		*child_node_flag_ptr = &pointers[i];
+	if (caa_unlikely(child_node_flag_v) && ptr)
+		*child_node_flag_v = ptr;
+	if (caa_unlikely(node_flag_ptr))
+		*node_flag_ptr = &pointers[i];
 	return ptr;
 }
 
@@ -328,19 +393,43 @@ void ja_linear_node_get_ith_pos(const struct cds_ja_type *type,
 static
 struct cds_ja_inode_flag *ja_pool_node_get_nth(const struct cds_ja_type *type,
 		struct cds_ja_inode *node,
+		struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_inode_flag ***child_node_flag_ptr,
+		struct cds_ja_inode_flag **child_node_flag_v,
+		struct cds_ja_inode_flag ***node_flag_ptr,
 		uint8_t n)
 {
 	struct cds_ja_inode *linear;
 
 	assert(type->type_class == RCU_JA_POOL);
-	/*
-	 * TODO: currently, we select the pool by highest bits. We
-	 * should support various encodings.
-	 */
-	linear = (struct cds_ja_inode *)
-		&node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
-	return ja_linear_node_get_nth(type, linear, child_node_flag_ptr, n);
+
+	switch (type->nr_pool_order) {
+	case 1:
+	{
+		unsigned long bitsel, index;
+
+		bitsel = ja_node_pool_1d_bitsel(node_flag);
+		assert(bitsel < CHAR_BIT);
+		index = ((unsigned long) n >> bitsel) & type->nr_pool_order;
+		linear = (struct cds_ja_inode *) &node->u.data[index << type->pool_size_order];
+		break;
+	}
+	case 2:
+	{
+		/*
+		 * TODO: currently, we select the pool by highest bits. We
+		 * should support various encodings.
+		 */
+		linear = (struct cds_ja_inode *)
+			&node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
+		break;
+	}
+	default:
+		linear = NULL;
+		assert(0);
+	}
+	return ja_linear_node_get_nth(type, linear, child_node_flag_ptr,
+		child_node_flag_v, node_flag_ptr, n);
 }
 
 static
@@ -357,17 +446,25 @@ static
 struct cds_ja_inode_flag *ja_pigeon_node_get_nth(const struct cds_ja_type *type,
 		struct cds_ja_inode *node,
 		struct cds_ja_inode_flag ***child_node_flag_ptr,
+		struct cds_ja_inode_flag **child_node_flag_v,
+		struct cds_ja_inode_flag ***node_flag_ptr,
 		uint8_t n)
 {
 	struct cds_ja_inode_flag **child_node_flag;
+	struct cds_ja_inode_flag *child_node_flag_read;
 
 	assert(type->type_class == RCU_JA_PIGEON);
 	child_node_flag = &((struct cds_ja_inode_flag **) node->u.data)[n];
+	child_node_flag_read = rcu_dereference(*child_node_flag);
 	dbg_printf("ja_pigeon_node_get_nth child_node_flag_ptr %p\n",
 		child_node_flag);
-	if (caa_unlikely(child_node_flag_ptr) && *child_node_flag)
+	if (caa_unlikely(child_node_flag_ptr) && child_node_flag_read)
 		*child_node_flag_ptr = child_node_flag;
-	return rcu_dereference(*child_node_flag);
+	if (caa_unlikely(child_node_flag_v) && child_node_flag_read)
+		*child_node_flag_v = child_node_flag_read;
+	if (caa_unlikely(node_flag_ptr))
+		*node_flag_ptr = child_node_flag;
+	return child_node_flag_read;
 }
 
 static
@@ -375,7 +472,7 @@ struct cds_ja_inode_flag *ja_pigeon_node_get_ith_pos(const struct cds_ja_type *t
 		struct cds_ja_inode *node,
 		uint8_t i)
 {
-	return ja_pigeon_node_get_nth(type, node, NULL, i);
+	return ja_pigeon_node_get_nth(type, node, NULL, NULL, NULL, i);
 }
 
 /*
@@ -383,8 +480,10 @@ struct cds_ja_inode_flag *ja_pigeon_node_get_ith_pos(const struct cds_ja_type *t
  * node_flag is already rcu_dereference'd.
  */
 static
-struct cds_ja_inode_flag * ja_node_get_nth(struct cds_ja_inode_flag *node_flag,
+struct cds_ja_inode_flag *ja_node_get_nth(struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_inode_flag ***child_node_flag_ptr,
+		struct cds_ja_inode_flag **child_node_flag,
+		struct cds_ja_inode_flag ***node_flag_ptr,
 		uint8_t n)
 {
 	unsigned int type_index;
@@ -399,13 +498,16 @@ struct cds_ja_inode_flag * ja_node_get_nth(struct cds_ja_inode_flag *node_flag,
 	switch (type->type_class) {
 	case RCU_JA_LINEAR:
 		return ja_linear_node_get_nth(type, node,
-				child_node_flag_ptr, n);
+				child_node_flag_ptr, child_node_flag,
+				node_flag_ptr, n);
 	case RCU_JA_POOL:
-		return ja_pool_node_get_nth(type, node,
-				child_node_flag_ptr, n);
+		return ja_pool_node_get_nth(type, node, node_flag,
+				child_node_flag_ptr, child_node_flag,
+				node_flag_ptr, n);
 	case RCU_JA_PIGEON:
 		return ja_pigeon_node_get_nth(type, node,
-				child_node_flag_ptr, n);
+				child_node_flag_ptr, child_node_flag,
+				node_flag_ptr, n);
 	default:
 		assert(0);
 		return (void *) -1UL;
@@ -473,6 +575,7 @@ int ja_linear_node_set_nth(const struct cds_ja_type *type,
 static
 int ja_pool_node_set_nth(const struct cds_ja_type *type,
 		struct cds_ja_inode *node,
+		struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_shadow_node *shadow_node,
 		uint8_t n,
 		struct cds_ja_inode_flag *child_node_flag)
@@ -480,8 +583,33 @@ int ja_pool_node_set_nth(const struct cds_ja_type *type,
 	struct cds_ja_inode *linear;
 
 	assert(type->type_class == RCU_JA_POOL);
-	linear = (struct cds_ja_inode *)
-		&node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
+
+	switch (type->nr_pool_order) {
+	case 1:
+	{
+		unsigned long bitsel, index;
+
+		bitsel = ja_node_pool_1d_bitsel(node_flag);
+		assert(bitsel < CHAR_BIT);
+		index = ((unsigned long) n >> bitsel) & type->nr_pool_order;
+		linear = (struct cds_ja_inode *) &node->u.data[index << type->pool_size_order];
+		break;
+	}
+	case 2:
+	{
+		/*
+		 * TODO: currently, we select the pool by highest bits. We
+		 * should support various encodings.
+		 */
+		linear = (struct cds_ja_inode *)
+			&node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
+		break;
+	}
+	default:
+		linear = NULL;
+		assert(0);
+	}
+
 	return ja_linear_node_set_nth(type, linear, shadow_node,
 			n, child_node_flag);
 }
@@ -511,6 +639,7 @@ int ja_pigeon_node_set_nth(const struct cds_ja_type *type,
 static
 int _ja_node_set_nth(const struct cds_ja_type *type,
 		struct cds_ja_inode *node,
+		struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_shadow_node *shadow_node,
 		uint8_t n,
 		struct cds_ja_inode_flag *child_node_flag)
@@ -520,7 +649,7 @@ int _ja_node_set_nth(const struct cds_ja_type *type,
 		return ja_linear_node_set_nth(type, node, shadow_node, n,
 				child_node_flag);
 	case RCU_JA_POOL:
-		return ja_pool_node_set_nth(type, node, shadow_node, n,
+		return ja_pool_node_set_nth(type, node, node_flag, shadow_node, n,
 				child_node_flag);
 	case RCU_JA_PIGEON:
 		return ja_pigeon_node_set_nth(type, node, shadow_node, n,
@@ -633,9 +762,147 @@ int _ja_node_clear_ptr(const struct cds_ja_type *type,
 	return 0;
 }
 
+/*
+ * Calculate bit distribution. Returns the bit (0 to 7) that splits the
+ * distribution in two sub-distributions containing as much elements one
+ * compared to the other.
+ */
+static
+unsigned int ja_node_sum_distribution_1d(enum ja_recompact mode,
+		struct cds_ja *ja,
+		unsigned int type_index,
+		const struct cds_ja_type *type,
+		struct cds_ja_inode *node,
+		struct cds_ja_shadow_node *shadow_node,
+		uint8_t n,
+		struct cds_ja_inode_flag *child_node_flag,
+		struct cds_ja_inode_flag **nullify_node_flag_ptr)
+{
+	uint8_t nr_one[JA_BITS_PER_BYTE];
+	unsigned int bitsel = 0, bit_i, overall_best_distance = UINT_MAX;
+	unsigned int distrib_nr_child = 0;
+
+	memset(nr_one, 0, sizeof(nr_one));
+
+	switch (type->type_class) {
+	case RCU_JA_LINEAR:
+	{
+		uint8_t nr_child =
+			ja_linear_node_get_nr_child(type, node);
+		unsigned int i;
+
+		for (i = 0; i < nr_child; i++) {
+			struct cds_ja_inode_flag *iter;
+			unsigned int bit;
+			uint8_t v;
+
+			ja_linear_node_get_ith_pos(type, node, i, &v, &iter);
+			if (!iter)
+				continue;
+			if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
+				continue;
+			for (bit = 0; bit < JA_BITS_PER_BYTE; bit++) {
+				if (v & (1U << bit))
+					nr_one[bit]++;
+			}
+			distrib_nr_child++;
+		}
+		break;
+	}
+	case RCU_JA_POOL:
+	{
+		unsigned int pool_nr;
+
+		for (pool_nr = 0; pool_nr < (1U << type->nr_pool_order); pool_nr++) {
+			struct cds_ja_inode *pool =
+				ja_pool_node_get_ith_pool(type,
+					node, pool_nr);
+			uint8_t nr_child =
+				ja_linear_node_get_nr_child(type, pool);
+			unsigned int j;
+
+			for (j = 0; j < nr_child; j++) {
+				struct cds_ja_inode_flag *iter;
+				unsigned int bit;
+				uint8_t v;
+
+				ja_linear_node_get_ith_pos(type, pool,
+						j, &v, &iter);
+				if (!iter)
+					continue;
+				if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
+					continue;
+				for (bit = 0; bit < JA_BITS_PER_BYTE; bit++) {
+					if (v & (1U << bit))
+						nr_one[bit]++;
+				}
+				distrib_nr_child++;
+			}
+		}
+		break;
+	}
+	case RCU_JA_PIGEON:
+	{
+		uint8_t nr_child;
+		unsigned int i;
+
+		assert(mode == JA_RECOMPACT_DEL);
+		nr_child = shadow_node->nr_child;
+		for (i = 0; i < nr_child; i++) {
+			struct cds_ja_inode_flag *iter;
+			unsigned int bit;
+
+			iter = ja_pigeon_node_get_ith_pos(type, node, i);
+			if (!iter)
+				continue;
+			if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
+				continue;
+			for (bit = 0; bit < JA_BITS_PER_BYTE; bit++) {
+				if (i & (1U << bit))
+					nr_one[bit]++;
+			}
+			distrib_nr_child++;
+		}
+		break;
+	}
+	case RCU_JA_NULL:
+		assert(mode == JA_RECOMPACT_ADD);
+		break;
+	default:
+		assert(0);
+		break;
+	}
+
+	if (mode == JA_RECOMPACT_ADD) {
+		unsigned int bit;
+
+		for (bit = 0; bit < JA_BITS_PER_BYTE; bit++) {
+			if (n & (1U << bit))
+				nr_one[bit]++;
+		}
+		distrib_nr_child++;
+	}
+
+	/*
+	 * The best bit selector is that for which the number of ones is
+	 * closest to half of the number of children in the
+	 * distribution.
+	 */
+	for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
+		unsigned int distance_to_best;
+
+		distance_to_best = abs_int(nr_one[bit_i] - (distrib_nr_child >> 1U));
+		if (distance_to_best < overall_best_distance) {
+			overall_best_distance = distance_to_best;
+			bitsel = bit_i;
+		}
+	}
+	dbg_printf("1 dimension pool bit selection: (%u)\n", bitsel);
+	return bitsel;
+}
+
 /*
  * ja_node_recompact_add: recompact a node, adding a new child.
- * TODO: for pool type, take selection bit(s) into account.
  * Return 0 on success, -EAGAIN if need to retry, or other negative
  * error value otherwise.
  */
@@ -690,7 +957,38 @@ retry:		/* for fallback */
 		new_node = alloc_cds_ja_node(new_type);
 		if (!new_node)
 			return -ENOMEM;
-		new_node_flag = ja_node_flag(new_node, new_type_index);
+
+		if (new_type->type_class == RCU_JA_POOL) {
+			switch (new_type->nr_pool_order) {
+			case 1:
+			{
+				unsigned int node_distrib_bitsel = 0;
+				node_distrib_bitsel =
+					ja_node_sum_distribution_1d(mode, ja,
+						old_type_index, old_type,
+						old_node, shadow_node,
+						n, child_node_flag,
+						nullify_node_flag_ptr);
+				assert(!((unsigned long) new_node & JA_POOL_1D_MASK));
+				new_node_flag = ja_node_flag_pool_1d(new_node,
+					new_type_index, node_distrib_bitsel);
+				break;
+			}
+			case 2:
+			{
+				/* TODO: pool order 2 in 2d */
+				assert(!((unsigned long) new_node & JA_POOL_1D_MASK));
+				assert(!((unsigned long) new_node & JA_POOL_2D_MASK));
+				new_node_flag = ja_node_flag(new_node, new_type_index);
+				break;
+			}
+			default:
+				assert(0);
+			}
+		} else {
+			new_node_flag = ja_node_flag(new_node, new_type_index);
+		}
+
 		dbg_printf("Recompact inherit lock from %p\n", shadow_node);
 		new_shadow_node = rcuja_shadow_set(ja->ht, new_node_flag, shadow_node, ja);
 		if (!new_shadow_node) {
@@ -726,7 +1024,7 @@ retry:		/* for fallback */
 				continue;
 			if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
 				continue;
-			ret = _ja_node_set_nth(new_type, new_node,
+			ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
 					new_shadow_node,
 					v, iter);
 			if (new_type->type_class == RCU_JA_POOL && ret) {
@@ -758,7 +1056,7 @@ retry:		/* for fallback */
 					continue;
 				if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
 					continue;
-				ret = _ja_node_set_nth(new_type, new_node,
+				ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
 						new_shadow_node,
 						v, iter);
 				if (new_type->type_class == RCU_JA_POOL
@@ -788,7 +1086,7 @@ retry:		/* for fallback */
 				continue;
 			if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
 				continue;
-			ret = _ja_node_set_nth(new_type, new_node,
+			ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
 					new_shadow_node,
 					i, iter);
 			if (new_type->type_class == RCU_JA_POOL && ret) {
@@ -807,9 +1105,12 @@ skip_copy:
 
 	if (mode == JA_RECOMPACT_ADD) {
 		/* add node */
-		ret = _ja_node_set_nth(new_type, new_node,
+		ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
 				new_shadow_node,
 				n, child_node_flag);
+		if (new_type->type_class == RCU_JA_POOL && ret) {
+			goto fallback_toosmall;
+		}
 		assert(!ret);
 	}
 	/* Return pointer to new recompacted node through old_node_flag_ptr */
@@ -870,7 +1171,7 @@ int ja_node_set_nth(struct cds_ja *ja,
 	node = ja_node_ptr(*node_flag);
 	type_index = ja_node_type(*node_flag);
 	type = &ja_types[type_index];
-	ret = _ja_node_set_nth(type, node, shadow_node,
+	ret = _ja_node_set_nth(type, node, *node_flag, shadow_node,
 			n, child_node_flag);
 	switch (ret) {
 	case -ENOSPC:
@@ -938,7 +1239,7 @@ struct cds_hlist_head cds_ja_lookup(struct cds_ja *ja, uint64_t key)
 		uint8_t iter_key;
 
 		iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (tree_depth - i - 1)));
-		node_flag = ja_node_get_nth(node_flag, NULL,
+		node_flag = ja_node_get_nth(node_flag, NULL, NULL, NULL,
 			iter_key);
 		dbg_printf("cds_ja_lookup iter key lookup %u finds node_flag %p\n",
 				(unsigned int) iter_key, node_flag);
@@ -965,6 +1266,8 @@ struct cds_hlist_head cds_ja_lookup(struct cds_ja *ja, uint64_t key)
  */
 static
 int ja_attach_node(struct cds_ja *ja,
+		struct cds_ja_inode_flag **attach_node_flag_ptr,
+		struct cds_ja_inode_flag *attach_node_flag,
 		struct cds_ja_inode_flag **node_flag_ptr,
 		struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_inode_flag *parent_node_flag,
@@ -1000,11 +1303,22 @@ int ja_attach_node(struct cds_ja *ja,
 		}
 	}
 
-	if (*node_flag_ptr != NULL) {
+	if (node_flag_ptr && ja_node_ptr(*node_flag_ptr)) {
 		/*
-		 * Attach point is non-NULL: it has been updated between
-		 * RCU lookup and lock acquisition. We need to re-try
-		 * lookup and attach.
+		 * Target node has been updated between RCU lookup and
+		 * lock acquisition. We need to re-try lookup and
+		 * attach.
+		 */
+		ret = -EAGAIN;
+		goto unlock_parent;
+	}
+
+	if (attach_node_flag_ptr && ja_node_ptr(*attach_node_flag_ptr) !=
+			ja_node_ptr(attach_node_flag)) {
+		/*
+		 * Target node has been updated between RCU lookup and
+		 * lock acquisition. We need to re-try lookup and
+		 * attach.
 		 */
 		ret = -EAGAIN;
 		goto unlock_parent;
@@ -1050,8 +1364,8 @@ int ja_attach_node(struct cds_ja *ja,
 
 	/* Publish new branch */
 	dbg_printf("Publish branch %p, replacing %p\n",
-		iter_node_flag, *node_flag_ptr);
-	rcu_assign_pointer(*node_flag_ptr, iter_node_flag);
+		iter_node_flag, *attach_node_flag_ptr);
+	rcu_assign_pointer(*attach_node_flag_ptr, iter_node_flag);
 
 	/* Success */
 	ret = 0;
@@ -1091,29 +1405,38 @@ end:
 static
 int ja_chain_node(struct cds_ja *ja,
 		struct cds_ja_inode_flag *parent_node_flag,
+		struct cds_ja_inode_flag **node_flag_ptr,
+		struct cds_ja_inode_flag *node_flag,
 		struct cds_hlist_head *head,
 		struct cds_ja_node *node)
 {
 	struct cds_ja_shadow_node *shadow_node;
+	int ret = 0;
 
 	shadow_node = rcuja_shadow_lookup_lock(ja->ht, parent_node_flag);
 	if (!shadow_node) {
-		dbg_printf("AGAIN3\n");
 		return -EAGAIN;
 	}
+	if (ja_node_ptr(*node_flag_ptr) != ja_node_ptr(node_flag)) {
+		ret = -EAGAIN;
+		goto end;
+	}
 	cds_hlist_add_head_rcu(&node->list, head);
+end:
 	rcuja_shadow_unlock(shadow_node);
-	return 0;
+	return ret;
 }
 
 int cds_ja_add(struct cds_ja *ja, uint64_t key,
 		struct cds_ja_node *new_node)
 {
 	unsigned int tree_depth, i;
-	struct cds_ja_inode_flag **node_flag_ptr;	/* in parent */
+	struct cds_ja_inode_flag **attach_node_flag_ptr,
+		**node_flag_ptr;
 	struct cds_ja_inode_flag *node_flag,
 		*parent_node_flag,
-		*parent2_node_flag;
+		*parent2_node_flag,
+		*attach_node_flag;
 	int ret;
 
 	if (caa_unlikely(key > ja->key_max)) {
@@ -1127,6 +1450,8 @@ retry:
 	parent2_node_flag = NULL;
 	parent_node_flag =
 		(struct cds_ja_inode_flag *) &ja->root;	/* Use root ptr address as key for mutex */
+	attach_node_flag_ptr = &ja->root;
+	attach_node_flag = rcu_dereference(ja->root);
 	node_flag_ptr = &ja->root;
 	node_flag = rcu_dereference(ja->root);
 
@@ -1134,11 +1459,14 @@ retry:
 	for (i = 1; i < tree_depth; i++) {
 		uint8_t iter_key;
 
-		dbg_printf("cds_ja_add iter node_flag_ptr %p node_flag %p\n",
-				*node_flag_ptr, node_flag);
+		dbg_printf("cds_ja_add iter attach_node_flag_ptr %p node_flag_ptr %p node_flag %p\n",
+				attach_node_flag_ptr, node_flag_ptr, node_flag);
 		if (!ja_node_ptr(node_flag)) {
-			ret = ja_attach_node(ja, node_flag_ptr,
-					parent_node_flag, parent2_node_flag,
+			ret = ja_attach_node(ja, attach_node_flag_ptr,
+					attach_node_flag,
+					node_flag_ptr,
+					parent_node_flag,
+					parent2_node_flag,
 					key, i, new_node);
 			if (ret == -EAGAIN || ret == -EEXIST)
 				goto retry;
@@ -1149,10 +1477,14 @@ retry:
 		parent2_node_flag = parent_node_flag;
 		parent_node_flag = node_flag;
 		node_flag = ja_node_get_nth(node_flag,
+			&attach_node_flag_ptr,
+			&attach_node_flag,
 			&node_flag_ptr,
 			iter_key);
-		dbg_printf("cds_ja_add iter key lookup %u finds node_flag %p node_flag_ptr %p\n",
-				(unsigned int) iter_key, node_flag, *node_flag_ptr);
+		dbg_printf("cds_ja_add iter key lookup %u finds node_flag %p attach_node_flag_ptr %p node_flag_ptr %p\n",
+				(unsigned int) iter_key, node_flag,
+				attach_node_flag_ptr,
+				node_flag_ptr);
 	}
 
 	/*
@@ -1160,14 +1492,18 @@ retry:
 	 * level, or chain it if key is already present.
 	 */
 	if (!ja_node_ptr(node_flag)) {
-		dbg_printf("cds_ja_add last node_flag_ptr %p node_flag %p\n",
-				*node_flag_ptr, node_flag);
-		ret = ja_attach_node(ja, node_flag_ptr, parent_node_flag,
+		dbg_printf("cds_ja_add attach_node_flag_ptr %p node_flag_ptr %p node_flag %p\n",
+				attach_node_flag_ptr, node_flag_ptr, node_flag);
+		ret = ja_attach_node(ja, attach_node_flag_ptr,
+				attach_node_flag,
+				node_flag_ptr, parent_node_flag,
 				parent2_node_flag, key, i, new_node);
 	} else {
 		ret = ja_chain_node(ja,
 			parent_node_flag,
-			(struct cds_hlist_head *) node_flag_ptr,
+			node_flag_ptr,
+			node_flag,
+			(struct cds_hlist_head *) attach_node_flag_ptr,
 			new_node);
 	}
 	if (ret == -EAGAIN || ret == -EEXIST)
@@ -1222,9 +1558,21 @@ int ja_detach_node(struct cds_ja *ja,
 			ret = -EAGAIN;
 			goto end;
 		}
-		assert(shadow_node->nr_child > 0);
 		shadow_nodes[nr_shadow++] = shadow_node;
-		if (shadow_node->nr_child == 1)
+
+		/*
+		 * Check if node has been removed between RCU
+		 * lookup and lock acquisition.
+		 */
+		assert(snapshot_ptr[i + 1]);
+		if (ja_node_ptr(*snapshot_ptr[i + 1])
+				!= ja_node_ptr(snapshot[i + 1])) {
+			ret = -ENOENT;
+			goto end;
+		}
+
+		assert(shadow_node->nr_child > 0);
+		if (shadow_node->nr_child == 1 && i > 1)
 			nr_clear++;
 		nr_branch++;
 		if (shadow_node->nr_child > 1 || i == 1) {
@@ -1236,10 +1584,23 @@ int ja_detach_node(struct cds_ja *ja,
 				goto end;
 			}
 			shadow_nodes[nr_shadow++] = shadow_node;
+
+			/*
+			 * Check if node has been removed between RCU
+			 * lookup and lock acquisition.
+			 */
+			assert(snapshot_ptr[i]);
+			if (ja_node_ptr(*snapshot_ptr[i])
+					!= ja_node_ptr(snapshot[i])) {
+				ret = -ENOENT;
+				goto end;
+			}
+
 			node_flag_ptr = snapshot_ptr[i + 1];
 			n = snapshot_n[i + 1];
 			parent_node_flag_ptr = snapshot_ptr[i];
 			parent_node_flag = snapshot[i];
+
 			if (i > 1) {
 				/*
 				 * Lock parent's parent, in case we need
@@ -1252,26 +1613,29 @@ int ja_detach_node(struct cds_ja *ja,
 					goto end;
 				}
 				shadow_nodes[nr_shadow++] = shadow_node;
+
+				/*
+				 * Check if node has been removed between RCU
+				 * lookup and lock acquisition.
+				 */
+				assert(snapshot_ptr[i - 1]);
+				if (ja_node_ptr(*snapshot_ptr[i - 1])
+						!= ja_node_ptr(snapshot[i - 1])) {
+					ret = -ENOENT;
+					goto end;
+				}
 			}
+
 			break;
 		}
 	}
 
-	/*
-	 * Check if node has been removed between RCU lookup and lock
-	 * acquisition.
-	 */
-	if (!*node_flag_ptr) {
-		ret = -ENOENT;
-		goto end;
-	}
-
 	/*
 	 * At this point, we want to delete all nodes that are about to
 	 * be removed from shadow_nodes (except the last one, which is
 	 * either the root or the parent of the upmost node with 1
-	 * child). OK to as to free lock here, because RCU read lock is
-	 * held, and free only performed in call_rcu.
+	 * child). OK to free lock here, because RCU read lock is held,
+	 * and free only performed in call_rcu.
 	 */
 
 	for (i = 0; i < nr_clear; i++) {
@@ -1307,29 +1671,48 @@ end:
 static
 int ja_unchain_node(struct cds_ja *ja,
 		struct cds_ja_inode_flag *parent_node_flag,
-		struct cds_hlist_head *head,
+		struct cds_ja_inode_flag **node_flag_ptr,
+		struct cds_ja_inode_flag *node_flag,
 		struct cds_ja_node *node)
 {
 	struct cds_ja_shadow_node *shadow_node;
 	struct cds_hlist_node *hlist_node;
-	int ret = 0, count = 0;
+	struct cds_hlist_head hlist_head;
+	int ret = 0, count = 0, found = 0;
 
 	shadow_node = rcuja_shadow_lookup_lock(ja->ht, parent_node_flag);
 	if (!shadow_node)
 		return -EAGAIN;
+	if (ja_node_ptr(*node_flag_ptr) != ja_node_ptr(node_flag)) {
+		ret = -EAGAIN;
+		goto end;
+	}
+	hlist_head.next = (struct cds_hlist_node *) ja_node_ptr(node_flag);
 	/*
 	 * Retry if another thread removed all but one of duplicates
-	 * since check (that was performed without lock).
+	 * since check (this check was performed without lock).
+	 * Ensure that the node we are about to remove is still in the
+	 * list (while holding lock).
 	 */
-	cds_hlist_for_each_rcu(hlist_node, head, list) {
+	cds_hlist_for_each_rcu(hlist_node, &hlist_head) {
+		if (count == 0) {
+			/* FIXME: currently a work-around */
+			hlist_node->prev = (struct cds_hlist_node *) node_flag_ptr;
+		}
 		count++;
+		if (hlist_node == &node->list)
+			found++;
 	}
-
-	if (count == 1) {
+	assert(found <= 1);
+	if (!found || count == 1) {
 		ret = -EAGAIN;
 		goto end;
 	}
 	cds_hlist_del_rcu(&node->list);
+	/*
+	 * Validate that we indeed removed the node from linked list.
+	 */
+	assert(ja_node_ptr(*node_flag_ptr) != (struct cds_ja_inode *) node);
 end:
 	rcuja_shadow_unlock(shadow_node);
 	return ret;
@@ -1346,7 +1729,8 @@ int cds_ja_del(struct cds_ja *ja, uint64_t key,
 	struct cds_ja_inode_flag **snapshot_ptr[JA_MAX_DEPTH];
 	uint8_t snapshot_n[JA_MAX_DEPTH];
 	struct cds_ja_inode_flag *node_flag;
-	struct cds_ja_inode_flag **prev_node_flag_ptr;
+	struct cds_ja_inode_flag **prev_node_flag_ptr,
+		**node_flag_ptr;
 	int nr_snapshot;
 	int ret;
 
@@ -1366,6 +1750,7 @@ retry:
 	snapshot[nr_snapshot++] = (struct cds_ja_inode_flag *) &ja->root;
 	node_flag = rcu_dereference(ja->root);
 	prev_node_flag_ptr = &ja->root;
+	node_flag_ptr = &ja->root;
 
 	/* Iterate on all internal levels */
 	for (i = 1; i < tree_depth; i++) {
@@ -1382,12 +1767,13 @@ retry:
 		snapshot[nr_snapshot++] = node_flag;
 		node_flag = ja_node_get_nth(node_flag,
 			&prev_node_flag_ptr,
+			NULL,
+			&node_flag_ptr,
 			iter_key);
 		dbg_printf("cds_ja_del iter key lookup %u finds node_flag %p, prev_node_flag_ptr %p\n",
 				(unsigned int) iter_key, node_flag,
 				prev_node_flag_ptr);
 	}
-
 	/*
 	 * We reached bottom of tree, try to find the node we are trying
 	 * to remove. Fail if we cannot find it.
@@ -1429,7 +1815,7 @@ retry:
 					snapshot_n, nr_snapshot, key, node);
 		} else {
 			ret = ja_unchain_node(ja, snapshot[nr_snapshot - 1],
-				&hlist_head, match);
+				node_flag_ptr, node_flag, match);
 		}
 	}
 	/*