Internal cleanup

[urcu.git] / urcu-qsbr.c

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 1ac553faefdf20ba1f775fe3af1fd49fd2e698f2..155505abc7843385fafef29de57509ceb096519c 100644 (file)
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -106,14 +106,20 @@ static void wait_gp(void)
                      NULL, NULL, 0);
 }
 
-static void wait_for_quiescent_state(void)
+static void update_counter_and_wait(void)
 {
        LIST_HEAD(qsreaders);
        int wait_loops = 0;
        struct rcu_reader *index, *tmp;
 
-       if (list_empty(&registry))
-               return;
+#if (BITS_PER_LONG < 64)
+       /* Switch parity: 1 -> 0, 0 -> 1 */
+       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+#else  /* !(BITS_PER_LONG < 64) */
+       /* Increment current G.P. */
+       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
+#endif /* !(BITS_PER_LONG < 64) */
+
        /*
         * Wait for each thread rcu_reader_qs_gp count to become 0.
         */
@@ -159,14 +165,6 @@ static void wait_for_quiescent_state(void)
  */
 
 #if (BITS_PER_LONG < 64)
-/*
- * called with rcu_gp_lock held.
- */
-static void switch_next_rcu_qparity(void)
-{
-       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
-}
-
 void synchronize_rcu(void)
 {
        unsigned long was_online;
@@ -189,20 +187,13 @@ void synchronize_rcu(void)
 
        mutex_lock(&rcu_gp_lock);
 
-       switch_next_rcu_qparity();      /* 0 -> 1 */
-
-       /*
-        * Must commit qparity update to memory before waiting for parity
-        * 0 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.
-        */
+       if (list_empty(&registry))
+               goto out;
 
        /*
         * Wait for previous parity to be empty of readers.
         */
-       wait_for_quiescent_state();     /* Wait readers in parity 0 */
+       update_counter_and_wait();      /* 0 -> 1, wait readers in parity 0 */
 
        /*
         * Must finish waiting for quiescent state for parity 0 before
@@ -212,21 +203,18 @@ void synchronize_rcu(void)
         * Ensured by STORE_SHARED and LOAD_SHARED.
         */
 
-       switch_next_rcu_qparity();      /* 1 -> 0 */
-
        /*
-        * Must commit qparity update to memory before waiting for parity
-        * 1 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.
+        * 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 previous parity to be empty of readers.
         */
-       wait_for_quiescent_state();     /* Wait readers in parity 1 */
-
+       update_counter_and_wait();      /* 1 -> 0, wait readers in parity 1 */
+out:
        mutex_unlock(&rcu_gp_lock);
 
        /*
@@ -254,8 +242,10 @@ void synchronize_rcu(void)
                STORE_SHARED(rcu_reader.ctr, 0);
 
        mutex_lock(&rcu_gp_lock);
-       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
-       wait_for_quiescent_state();
+       if (list_empty(&registry))
+               goto out;
+       update_counter_and_wait();
+out:
        mutex_unlock(&rcu_gp_lock);
 
        if (was_online)