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: Paul 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>

diff --git a/lib/assoc_array.c b/lib/assoc_array.c
index b77d51d..c6659cb 100644 (file)
--- a/lib/assoc_array.c
+++ b/lib/assoc_array.c
@@ -38,12 +38,10 @@ begin_node:
        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 @@ begin_node:
         */
        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 @@ begin_node:
 
 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 @@ continue_node:
 
 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 @@ jumped:
 
 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 @@ consider_node:
        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 @@ follow_shortcut:
        } 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;
                }