rcuja fix: perform lookup in attach node

Handles case where the existing location is not yet reserved. Therefore,
a pointer check cannot be used to check if it has been concurrently
populated. A full-blown lookup is therefore required.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/rcuja/rcuja.c b/rcuja/rcuja.c
index 84c1fb73c26afdc3bc09b0bd037edf6a728d4027..b0d33221ae6c730ed756453b655dba5564fe38b7 100644 (file)
--- a/rcuja/rcuja.c
+++ b/rcuja/rcuja.c
@@ -1674,6 +1674,27 @@ int ja_attach_node(struct cds_ja *ja,
                goto unlock_parent;
        }
 
+       /*
+        * Perform a lookup query to handle the case where
+        * old_node_flag_ptr is NULL. We cannot use it to check if the
+        * node has been populated between RCU lookup and mutex
+        * acquisition.
+        */
+       if (!old_node_flag_ptr) {
+               uint8_t iter_key;
+               struct cds_ja_inode_flag *lookup_node_flag;
+               struct cds_ja_inode_flag **lookup_node_flag_ptr;
+
+               iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (ja->tree_depth - level)));
+               lookup_node_flag = ja_node_get_nth(attach_node_flag,
+                       &lookup_node_flag_ptr,
+                       iter_key);
+               if (lookup_node_flag) {
+                       ret = -EEXIST;
+                       goto unlock_parent;
+               }
+       }
+
        if (attach_node_flag_ptr && ja_node_ptr(*attach_node_flag_ptr) !=
                        ja_node_ptr(attach_node_flag)) {
                /*
@@ -1701,8 +1722,10 @@ int ja_attach_node(struct cds_ja *ja,
                        iter_key,
                        iter_node_flag,
                        NULL, i);
-               if (ret)
+               if (ret) {
+                       dbg_printf("branch creation error %d\n", ret);
                        goto check_error;
+               }
                created_nodes[nr_created_nodes++] = iter_dest_node_flag;
                iter_node_flag = iter_dest_node_flag;
        }
@@ -1726,8 +1749,10 @@ int ja_attach_node(struct cds_ja *ja,
                        iter_key,
                        iter_node_flag,
                        shadow_node, level - 1);
-               if (ret)
+               if (ret) {
+                       dbg_printf("branch publish error %d\n", ret);
                        goto check_error;
+               }
                /*
                 * Attach branch
                 */