Fix: move wait loop increment before first conditional block

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index da6839f0c25b88b4262e9a615bd197220789c185..ae3490f7cb2cdc1f7cdb1d26f77c0ee22620e9eb 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -53,15 +53,33 @@
 /*
  * If a reader is really non-cooperative and refuses to commit its
  * rcu_active_readers count to memory (there is no barrier in the reader
- * per-se), kick it after a few loops waiting for it.
+ * per-se), kick it after 10 loops waiting for it.
  */
-#define KICK_READER_LOOPS 10000
+#define KICK_READER_LOOPS      10
 
 /*
  * Active attempts to check for reader Q.S. before calling futex().
  */
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
+/*
+ * RCU_MEMBARRIER is only possibly available on Linux.
+ */
+#if defined(RCU_MEMBARRIER) && defined(__linux__)
+#include <urcu/syscall-compat.h>
+#endif
+
+/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
+#ifdef SYS_membarrier
+# define membarrier(...)               syscall(SYS_membarrier, __VA_ARGS__)
+#else
+# define membarrier(...)               -ENOSYS
+#endif
+
+#define MEMBARRIER_EXPEDITED           (1 << 0)
+#define MEMBARRIER_DELAYED             (1 << 1)
+#define MEMBARRIER_QUERY               (1 << 16)
+
 #ifdef RCU_MEMBARRIER
 static int init_done;
 int rcu_has_sys_membarrier;
@@ -83,7 +101,7 @@ void __attribute__((destructor)) rcu_exit(void);
 #endif
 
 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
-struct urcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
+struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 
 /*
  * Written to only by each individual reader. Read by both the reader and the
@@ -91,11 +109,6 @@ struct urcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
  */
 DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
 
-#ifdef DEBUG_YIELD
-unsigned int rcu_yield_active;
-DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
-#endif
-
 static CDS_LIST_HEAD(registry);
 
 /*
@@ -139,7 +152,7 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 static void smp_mb_master(int group)
 {
        if (caa_likely(rcu_has_sys_membarrier))
-               membarrier(MEMBARRIER_EXPEDITED);
+               (void) membarrier(MEMBARRIER_EXPEDITED);
        else
                cmm_smp_mb();
 }
@@ -217,8 +230,11 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                        struct cds_list_head *cur_snap_readers,
                        struct cds_list_head *qsreaders)
 {
-       int wait_loops = 0;
+       unsigned int wait_loops = 0;
        struct rcu_reader *index, *tmp;
+#ifdef HAS_INCOHERENT_CACHES
+       unsigned int wait_gp_loops = 0;
+#endif /* HAS_INCOHERENT_CACHES */
 
        /*
         * Wait for each thread URCU_TLS(rcu_reader).ctr to either
@@ -226,8 +242,9 @@ static void wait_for_readers(struct cds_list_head *input_readers,
         * rcu_gp.ctr value.
         */
        for (;;) {
-               wait_loops++;
-               if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+               if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
+                       wait_loops++;
+               if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
                        uatomic_dec(&rcu_gp.futex);
                        /* Write futex before read reader_gp */
                        smp_mb_master(RCU_MB_GROUP);
@@ -258,14 +275,14 @@ static void wait_for_readers(struct cds_list_head *input_readers,
 
 #ifndef HAS_INCOHERENT_CACHES
                if (cds_list_empty(input_readers)) {
-                       if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
                                smp_mb_master(RCU_MB_GROUP);
                                uatomic_set(&rcu_gp.futex, 0);
                        }
                        break;
                } else {
-                       if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
+                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
                                wait_gp();
                        else
                                caa_cpu_relax();
@@ -277,22 +294,21 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                 * for too long.
                 */
                if (cds_list_empty(input_readers)) {
-                       if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
                                smp_mb_master(RCU_MB_GROUP);
                                uatomic_set(&rcu_gp.futex, 0);
                        }
                        break;
                } else {
-                       switch (wait_loops) {
-                       case RCU_QS_ACTIVE_ATTEMPTS:
-                               wait_gp();
-                               break; /* only escape switch */
-                       case KICK_READER_LOOPS:
+                       if (wait_gp_loops == KICK_READER_LOOPS) {
                                smp_mb_master(RCU_MB_GROUP);
-                               wait_loops = 0;
-                               break; /* only escape switch */
-                       default:
+                               wait_gp_loops = 0;
+                       }
+                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+                               wait_gp();
+                               wait_gp_loops++;
+                       } else {
                                caa_cpu_relax();
                        }
                }
@@ -495,14 +511,14 @@ void rcu_init(void)
 
 void rcu_exit(void)
 {
-       struct sigaction act;
-       int ret;
-
-       ret = sigaction(SIGRCU, NULL, &act);
-       if (ret)
-               urcu_die(errno);
-       assert(act.sa_sigaction == sigrcu_handler);
-       assert(cds_list_empty(&registry));
+       /*
+        * Don't unregister the SIGRCU signal handler anymore, because
+        * call_rcu threads could still be using it shortly before the
+        * application exits.
+        * Assertion disabled because call_rcu threads are now rcu
+        * readers, and left running at exit.
+        * assert(cds_list_empty(&registry));
+        */
 }
 
 #endif /* #ifdef RCU_SIGNAL */