Fix powerpc uatomic 4-byte cmpxchg (cmpd -> cmpw)

[urcu.git] / urcu-qsbr.c

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 84789f2ebfdd4fa89def6fb56274595739a51d02..0e1252fdbba707e4515cbbabe8c8a837a6408c79 100644 (file)
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -120,6 +120,21 @@ static void update_counter_and_wait(void)
        STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
 #endif /* !(BITS_PER_LONG < 64) */
 
+       /*
+        * 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();
+
+       /*
+        * Adding a smp_mb() which is _not_ formally required, but makes the
+        * model easier to understand. It does not have a big performance impact
+        * anyway, given this is the write-side.
+        */
+       smp_mb();
+
        /*
         * Wait for each thread rcu_reader_qs_gp count to become 0.
         */
@@ -131,9 +146,9 @@ static void update_counter_and_wait(void)
                        smp_mb();
                }
 
-               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);
                }
 
                if (list_empty(&registry)) {
@@ -197,11 +212,12 @@ 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
@@ -289,7 +305,7 @@ void rcu_register_thread(void)
        assert(rcu_reader.ctr == 0);
 
        mutex_lock(&rcu_gp_lock);
-       list_add(&rcu_reader.head, &registry);
+       list_add(&rcu_reader.node, &registry);
        mutex_unlock(&rcu_gp_lock);
        _rcu_thread_online();
 }
@@ -302,7 +318,7 @@ void rcu_unregister_thread(void)
         */
        _rcu_thread_offline();
        mutex_lock(&rcu_gp_lock);
-       list_del(&rcu_reader.head);
+       list_del(&rcu_reader.node);
        mutex_unlock(&rcu_gp_lock);
 }