add missing comment to wfstack.c

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index bb6629c718086a9800a22a4d3ab21685b27c26a5..918d2742a0429683c11e42c60c77187bc908e862 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -3,7 +3,7 @@
  *
  * Userspace RCU library
  *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  *
  * This library is free software; you can redistribute it and/or
@@ -154,7 +154,7 @@ static void force_mb_all_readers(void)
         * safe and don't assume anything : we use smp_mc() to make sure the
         * cache flush is enforced.
         */
-       list_for_each_entry(index, &registry, head) {
+       list_for_each_entry(index, &registry, node) {
                STORE_SHARED(index->need_mb, 1);
                pthread_kill(index->tid, SIGRCU);
        }
@@ -171,7 +171,7 @@ static void force_mb_all_readers(void)
         * relevant bug report.  For Linux kernels, we recommend getting
         * the Linux Test Project (LTP).
         */
-       list_for_each_entry(index, &registry, head) {
+       list_for_each_entry(index, &registry, node) {
                while (LOAD_SHARED(index->need_mb)) {
                        pthread_kill(index->tid, SIGRCU);
                        poll(NULL, 0, 1);
@@ -208,16 +208,14 @@ void update_counter_and_wait(void)
        STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 
        /*
-        * Must commit qparity update to memory before waiting for other parity
-        * quiescent state. Failure to do so could result in the writer waiting
-        * forever while new readers are always accessing data (no progress).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
+        * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+        * state. Failure to do so could result in the writer waiting forever
+        * while new readers are always accessing data (no progress). Enforce
+        * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
         */
+       barrier();
 
        /*
-        * Enforce compiler-order of store to rcu_gp_ctr before before
-        * load rcu_reader ctr.
-        * This ensures synchronize_rcu() cannot be starved by readers.
         *
         * Adding a smp_mb() which is _not_ formally required, but makes the
         * model easier to understand. It does not have a big performance impact
@@ -236,9 +234,9 @@ void update_counter_and_wait(void)
                        smp_mb_master(RCU_MB_GROUP);
                }
 
-               list_for_each_entry_safe(index, tmp, &registry, head) {
+               list_for_each_entry_safe(index, tmp, &registry, node) {
                        if (!rcu_gp_ongoing(&index->ctr))
-                               list_move(&index->head, &qsreaders);
+                               list_move(&index->node, &qsreaders);
                }
 
 #ifndef HAS_INCOHERENT_CACHES
@@ -306,11 +304,12 @@ void synchronize_rcu(void)
 
        /*
         * Must finish waiting for quiescent state for parity 0 before
-        * committing qparity update to memory. Failure to do so could result in
-        * the writer waiting forever while new readers are always accessing
-        * data (no progress).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
+        * committing next rcu_gp_ctr update to memory. Failure to do so could
+        * result in the writer waiting forever while new readers are always
+        * accessing data (no progress).  Enforce compiler-order of load
+        * rcu_reader ctr before store to rcu_gp_ctr.
         */
+       barrier();
 
        /*
         * Adding a smp_mb() which is _not_ formally required, but makes the
@@ -354,14 +353,14 @@ void rcu_register_thread(void)
 
        mutex_lock(&rcu_gp_lock);
        rcu_init();     /* In case gcc does not support constructor attribute */
-       list_add(&rcu_reader.head, &registry);
+       list_add(&rcu_reader.node, &registry);
        mutex_unlock(&rcu_gp_lock);
 }
 
 void rcu_unregister_thread(void)
 {
        mutex_lock(&rcu_gp_lock);
-       list_del(&rcu_reader.head);
+       list_del(&rcu_reader.node);
        mutex_unlock(&rcu_gp_lock);
 }