urcu-qsbr: document compiler barrier

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index e93170d749b4c939884840767febcc3e3d820997..b8567555d09ecbb22547aa6f236392d439eea871 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -67,7 +67,7 @@ int gp_futex;
  * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
  * Written to only by writer with mutex taken. Read by both writer and readers.
  */
-long rcu_gp_ctr = RCU_GP_COUNT;
+unsigned long rcu_gp_ctr = RCU_GP_COUNT;
 
 /*
  * Written to only by each individual reader. Read by both the reader and the
@@ -99,9 +99,9 @@ static void mutex_lock(pthread_mutex_t *mutex)
                        perror("Error in pthread mutex lock");
                        exit(-1);
                }
-               if (rcu_reader.need_mb) {
+               if (LOAD_SHARED(rcu_reader.need_mb)) {
                        smp_mb();
-                       rcu_reader.need_mb = 0;
+                       _STORE_SHARED(rcu_reader.need_mb, 0);
                        smp_mb();
                }
                poll(NULL,0,10);
@@ -121,7 +121,7 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 }
 
 #ifdef RCU_MEMBARRIER
-static void smp_mb_heavy(void)
+static void smp_mb_master(int group)
 {
        if (likely(has_sys_membarrier))
                membarrier(MEMBARRIER_EXPEDITED);
@@ -131,7 +131,7 @@ static void smp_mb_heavy(void)
 #endif
 
 #ifdef RCU_MB
-static void smp_mb_heavy(void)
+static void smp_mb_master(int group)
 {
        smp_mb();
 }
@@ -155,8 +155,7 @@ static void force_mb_all_readers(void)
         * cache flush is enforced.
         */
        list_for_each_entry(index, &registry, head) {
-               index->need_mb = 1;
-               smp_mc();       /* write need_mb before sending the signal */
+               STORE_SHARED(index->need_mb, 1);
                pthread_kill(index->tid, SIGRCU);
        }
        /*
@@ -173,7 +172,7 @@ static void force_mb_all_readers(void)
         * the Linux Test Project (LTP).
         */
        list_for_each_entry(index, &registry, head) {
-               while (index->need_mb) {
+               while (LOAD_SHARED(index->need_mb)) {
                        pthread_kill(index->tid, SIGRCU);
                        poll(NULL, 0, 1);
                }
@@ -181,7 +180,7 @@ static void force_mb_all_readers(void)
        smp_mb();       /* read ->need_mb before ending the barrier */
 }
 
-static void smp_mb_heavy(void)
+static void smp_mb_master(int group)
 {
        force_mb_all_readers();
 }
@@ -193,7 +192,7 @@ static void smp_mb_heavy(void)
 static void wait_gp(void)
 {
        /* Read reader_gp before read futex */
-       smp_mb_heavy();
+       smp_mb_master(RCU_MB_GROUP);
        if (uatomic_read(&gp_futex) == -1)
                futex_async(&gp_futex, FUTEX_WAIT, -1,
                      NULL, NULL, 0);
@@ -205,7 +204,7 @@ void update_counter_and_wait(void)
        int wait_loops = 0;
        struct rcu_reader *index, *tmp;
 
-       /* Switch parity: 1 -> 0, 0 -> 1 */
+       /* Switch parity: 0 -> 1, 1 -> 0 */
        STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 
        /*
@@ -230,11 +229,11 @@ void update_counter_and_wait(void)
                if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                        uatomic_dec(&gp_futex);
                        /* Write futex before read reader_gp */
-                       smp_mb_heavy();
+                       smp_mb_master(RCU_MB_GROUP);
                }
 
                list_for_each_entry_safe(index, tmp, &registry, head) {
-                       if (!rcu_old_gp_ongoing(&index->ctr))
+                       if (!rcu_gp_ongoing(&index->ctr))
                                list_move(&index->head, &qsreaders);
                }
 
@@ -242,7 +241,7 @@ void update_counter_and_wait(void)
                if (list_empty(&registry)) {
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
-                               smp_mb_heavy();
+                               smp_mb_master(RCU_MB_GROUP);
                                uatomic_set(&gp_futex, 0);
                        }
                        break;
@@ -260,7 +259,7 @@ void update_counter_and_wait(void)
                if (list_empty(&registry)) {
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
-                               smp_mb_heavy();
+                               smp_mb_master(RCU_MB_GROUP);
                                uatomic_set(&gp_futex, 0);
                        }
                        break;
@@ -270,7 +269,7 @@ void update_counter_and_wait(void)
                                wait_gp();
                                break; /* only escape switch */
                        case KICK_READER_LOOPS:
-                               smp_mb_heavy();
+                               smp_mb_master(RCU_MB_GROUP);
                                wait_loops = 0;
                                break; /* only escape switch */
                        default:
@@ -294,7 +293,7 @@ void synchronize_rcu(void)
         * where new ptr points to. Must be done within rcu_gp_lock because it
         * iterates on reader threads.*/
        /* Write new ptr before changing the qparity */
-       smp_mb_heavy();
+       smp_mb_master(RCU_MB_GROUP);
 
        /*
         * Wait for previous parity to be empty of readers.
@@ -324,7 +323,7 @@ void synchronize_rcu(void)
        /* Finish waiting for reader threads before letting the old ptr being
         * freed. Must be done within rcu_gp_lock because it iterates on reader
         * threads. */
-       smp_mb_heavy();
+       smp_mb_master(RCU_MB_GROUP);
 out:
        mutex_unlock(&rcu_gp_lock);
 }
@@ -347,7 +346,7 @@ void rcu_register_thread(void)
 {
        rcu_reader.tid = pthread_self();
        assert(rcu_reader.need_mb == 0);
-       assert(rcu_reader.ctr == 0);
+       assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
 
        mutex_lock(&rcu_gp_lock);
        rcu_init();     /* In case gcc does not support constructor attribute */
@@ -382,7 +381,7 @@ static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
         * executed on.
         */
        smp_mb();
-       rcu_reader.need_mb = 0;
+       _STORE_SHARED(rcu_reader.need_mb, 0);
        smp_mb();
 }