Fix: urcu: futex wait: handle spurious futex wakeups

[urcu.git] / src / urcu.c

diff --git a/src/urcu.c b/src/urcu.c
index c36119aeb466673c03c810dc2ea372eea568f10f..a8c033a0bb7c960755428ec7a3caeff6b3f309e7 100644 (file)
--- a/src/urcu.c
+++ b/src/urcu.c
@@ -23,6 +23,7 @@
  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  */
 
+#define URCU_NO_COMPAT_IDENTIFIERS
 #define _BSD_SOURCE
 #define _LGPL_SOURCE
 #define _DEFAULT_SOURCE
@@ -37,6 +38,7 @@
 #include <stdbool.h>
 #include <poll.h>
 
+#include <urcu/config.h>
 #include <urcu/arch.h>
 #include <urcu/wfcqueue.h>
 #include <urcu/map/urcu.h>
@@ -92,7 +94,7 @@ static int urcu_memb_has_sys_membarrier_private_expedited;
  * uninitialized variable.
  */
 int urcu_memb_has_sys_membarrier = 0;
-__attribute__((alias("urcu_memb_has_sys_membarrier")))
+URCU_ATTR_ALIAS("urcu_memb_has_sys_membarrier")
 extern int rcu_has_sys_membarrier_memb;
 #endif
 
@@ -103,7 +105,7 @@ void __attribute__((constructor)) rcu_init(void);
 void rcu_init(void)
 {
 }
-__attribute__((alias(urcu_stringify(rcu_init))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 void alias_rcu_init(void);
 #endif
 
@@ -130,7 +132,7 @@ static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
  */
 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 struct urcu_gp rcu_gp = { .ctr = URCU_GP_COUNT };
-__attribute__((alias(urcu_stringify(rcu_gp))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_gp))
 extern struct urcu_gp alias_rcu_gp;
 
 /*
@@ -138,8 +140,7 @@ extern struct urcu_gp alias_rcu_gp;
  * writers.
  */
 DEFINE_URCU_TLS(struct urcu_reader, rcu_reader);
-__attribute__((alias(urcu_stringify(rcu_reader))))
-extern struct urcu_reader alias_rcu_reader;
+DEFINE_URCU_TLS_ALIAS(struct urcu_reader, rcu_reader, alias_rcu_reader);
 
 static CDS_LIST_HEAD(registry);
 
@@ -265,17 +266,25 @@ static void wait_gp(void)
        smp_mb_master();
        /* Temporarily unlock the registry lock. */
        mutex_unlock(&rcu_registry_lock);
-       if (uatomic_read(&rcu_gp.futex) != -1)
-               goto end;
-       while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
-                       NULL, NULL, 0)) {
+       while (uatomic_read(&rcu_gp.futex) == -1) {
+               if (!futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
+                       /*
+                        * Prior queued wakeups queued by unrelated code
+                        * using the same address can cause futex wait to
+                        * return 0 even through the futex value is still
+                        * -1 (spurious wakeups). Check the value again
+                        * in user-space to validate whether it really
+                        * differs from -1.
+                        */
+                       continue;
+               }
                switch (errno) {
-               case EWOULDBLOCK:
+               case EAGAIN:
                        /* Value already changed. */
                        goto end;
                case EINTR:
                        /* Retry if interrupted by signal. */
-                       break;  /* Get out of switch. */
+                       break;  /* Get out of switch. Check again. */
                default:
                        /* Unexpected error. */
                        urcu_die(errno);
@@ -515,7 +524,7 @@ out:
         */
        urcu_wake_all_waiters(&waiters);
 }
-__attribute__((alias(urcu_stringify(synchronize_rcu))))
+URCU_ATTR_ALIAS(urcu_stringify(synchronize_rcu))
 void alias_synchronize_rcu();
 
 /*
@@ -526,21 +535,21 @@ void rcu_read_lock(void)
 {
        _rcu_read_lock();
 }
-__attribute__((alias(urcu_stringify(rcu_read_lock))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_read_lock))
 void alias_rcu_read_lock();
 
 void rcu_read_unlock(void)
 {
        _rcu_read_unlock();
 }
-__attribute__((alias(urcu_stringify(rcu_read_unlock))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_read_unlock))
 void alias_rcu_read_unlock();
 
 int rcu_read_ongoing(void)
 {
        return _rcu_read_ongoing();
 }
-__attribute__((alias(urcu_stringify(rcu_read_ongoing))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_read_ongoing))
 void alias_rcu_read_ongoing();
 
 void rcu_register_thread(void)
@@ -556,7 +565,7 @@ void rcu_register_thread(void)
        cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
        mutex_unlock(&rcu_registry_lock);
 }
-__attribute__((alias(urcu_stringify(rcu_register_thread))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_register_thread))
 void alias_rcu_register_thread();
 
 void rcu_unregister_thread(void)
@@ -567,7 +576,7 @@ void rcu_unregister_thread(void)
        cds_list_del(&URCU_TLS(rcu_reader).node);
        mutex_unlock(&rcu_registry_lock);
 }
-__attribute__((alias(urcu_stringify(rcu_unregister_thread))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_unregister_thread))
 void alias_rcu_unregister_thread();
 
 #ifdef RCU_MEMBARRIER
@@ -616,12 +625,14 @@ void rcu_init(void)
        init_done = 1;
        rcu_sys_membarrier_init();
 }
-__attribute__((alias(urcu_stringify(rcu_init))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 void alias_rcu_init(void);
 #endif
 
 #ifdef RCU_SIGNAL
-static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
+static void sigrcu_handler(int signo __attribute__((unused)),
+               siginfo_t *siginfo __attribute__((unused)),
+               void *context __attribute__((unused)))
 {
        /*
         * Executing this cmm_smp_mb() is the only purpose of this signal handler.
@@ -657,7 +668,7 @@ void rcu_init(void)
        if (ret)
                urcu_die(errno);
 }
-__attribute__((alias(urcu_stringify(rcu_init))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
 void alias_rcu_init(void);
 
 void rcu_exit(void)
@@ -671,7 +682,7 @@ void rcu_exit(void)
         * assert(cds_list_empty(&registry));
         */
 }
-__attribute__((alias(urcu_stringify(rcu_exit))))
+URCU_ATTR_ALIAS(urcu_stringify(rcu_exit))
 void alias_rcu_exit(void);
 
 #endif /* #ifdef RCU_SIGNAL */