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Commit 516df050 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

lib/assoc_array: Remove smp_read_barrier_depends() 



Now that smp_read_barrier_depends() is implied by READ_ONCE(), the several
smp_read_barrier_depends() calls may be removed from lib/assoc_array.c.
This commit makes this change and marks the READ_ONCE() calls that head
address dependencies.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: David Howells <dhowells@redhat.com>
parent 243d1a79

lib/assoc_array.c

+12 −25
Original line number Diff line number Diff line
@@ -38,12 +38,10 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, 
	if (assoc_array_ptr_is_shortcut(cursor)) {

		/* Descend through a shortcut */

		shortcut = assoc_array_ptr_to_shortcut(cursor);

		smp_read_barrier_depends();

		cursor = READ_ONCE(shortcut->next_node);

		cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */

	}



	node = assoc_array_ptr_to_node(cursor);

	smp_read_barrier_depends();

	slot = 0;



	/* We perform two passes of each node.
@@ -55,15 +53,12 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, 
	 */

	has_meta = 0;

	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {

		ptr = READ_ONCE(node->slots[slot]);

		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */

		has_meta |= (unsigned long)ptr;

		if (ptr && assoc_array_ptr_is_leaf(ptr)) {

			/* We need a barrier between the read of the pointer

			 * and dereferencing the pointer - but only if we are

			 * actually going to dereference it.

			/* We need a barrier between the read of the pointer,

			 * which is supplied by the above READ_ONCE().

			 */

			smp_read_barrier_depends();



			/* Invoke the callback */

			ret = iterator(assoc_array_ptr_to_leaf(ptr),

				       iterator_data);
@@ -86,10 +81,8 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, 


continue_node:

	node = assoc_array_ptr_to_node(cursor);

	smp_read_barrier_depends();



	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {

		ptr = READ_ONCE(node->slots[slot]);

		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */

		if (assoc_array_ptr_is_meta(ptr)) {

			cursor = ptr;

			goto begin_node;
@@ -98,16 +91,15 @@ static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, 


finished_node:

	/* Move up to the parent (may need to skip back over a shortcut) */

	parent = READ_ONCE(node->back_pointer);

	parent = READ_ONCE(node->back_pointer); /* Address dependency. */

	slot = node->parent_slot;

	if (parent == stop)

		return 0;



	if (assoc_array_ptr_is_shortcut(parent)) {

		shortcut = assoc_array_ptr_to_shortcut(parent);

		smp_read_barrier_depends();

		cursor = parent;

		parent = READ_ONCE(shortcut->back_pointer);

		parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */

		slot = shortcut->parent_slot;

		if (parent == stop)

			return 0;
@@ -147,7 +139,7 @@ int assoc_array_iterate(const struct assoc_array *array, 
					void *iterator_data),

			void *iterator_data)

{

	struct assoc_array_ptr *root = READ_ONCE(array->root);

	struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */



	if (!root)

		return 0;
@@ -194,7 +186,7 @@ assoc_array_walk(const struct assoc_array *array, 


	pr_devel("-->%s()\n", __func__);



	cursor = READ_ONCE(array->root);

	cursor = READ_ONCE(array->root);  /* Address dependency. */

	if (!cursor)

		return assoc_array_walk_tree_empty;
@@ -216,11 +208,9 @@ assoc_array_walk(const struct assoc_array *array, 


consider_node:

	node = assoc_array_ptr_to_node(cursor);

	smp_read_barrier_depends();



	slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);

	slot &= ASSOC_ARRAY_FAN_MASK;

	ptr = READ_ONCE(node->slots[slot]);

	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */



	pr_devel("consider slot %x [ix=%d type=%lu]\n",

		 slot, level, (unsigned long)ptr & 3);
@@ -254,7 +244,6 @@ assoc_array_walk(const struct assoc_array *array, 
	cursor = ptr;

follow_shortcut:

	shortcut = assoc_array_ptr_to_shortcut(cursor);

	smp_read_barrier_depends();

	pr_devel("shortcut to %d\n", shortcut->skip_to_level);

	sc_level = level + ASSOC_ARRAY_LEVEL_STEP;

	BUG_ON(sc_level > shortcut->skip_to_level);
@@ -294,7 +283,7 @@ assoc_array_walk(const struct assoc_array *array, 
	} while (sc_level < shortcut->skip_to_level);



	/* The shortcut matches the leaf's index to this point. */

	cursor = READ_ONCE(shortcut->next_node);

	cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */

	if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {

		level = sc_level;

		goto jumped;
@@ -331,20 +320,18 @@ void *assoc_array_find(const struct assoc_array *array, 
		return NULL;



	node = result.terminal_node.node;

	smp_read_barrier_depends();



	/* If the target key is available to us, it's has to be pointed to by

	 * the terminal node.

	 */

	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {

		ptr = READ_ONCE(node->slots[slot]);

		ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */

		if (ptr && assoc_array_ptr_is_leaf(ptr)) {

			/* We need a barrier between the read of the pointer

			 * and dereferencing the pointer - but only if we are

			 * actually going to dereference it.

			 */

			leaf = assoc_array_ptr_to_leaf(ptr);

			smp_read_barrier_depends();

			if (ops->compare_object(leaf, index_key))

				return (void *)leaf;

		}