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>

1 files changed, 12 insertions, 25 deletions

diff --git a/lib/assoc_array.c b/lib/assoc_array.c
index b77d51da8c73..c6659cb37033 100644
--- 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;
                 }