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(®istry))
- return;
+#if (BITS_PER_LONG < 64)
+ /* Switch parity: 0 -> 1, 1 -> 0 */
+ 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.
*/
*/
#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;
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(®istry))
+ 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
* 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);
/*
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(®istry))
+ goto out;
+ update_counter_and_wait();
+out:
mutex_unlock(&rcu_gp_lock);
if (was_online)