Fix signal handler installation

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index efbb4b7890a71524fa8264877f3da63565291591..c07df2e8cf21384a07da3bb47066cd2b2bb44084 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -36,6 +36,17 @@
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu.h"
 
+#ifndef DEBUG_FULL_MB
+void __attribute__((constructor)) urcu_init(void);
+void __attribute__((destructor)) urcu_exit(void);
+#else
+static inline urcu_init(void)
+{
+}
+#endif
+
+int init_done;
+
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /*
@@ -249,12 +260,11 @@ void synchronize_rcu(void)
         */
 
        /*
-        * Current RCU formal verification model assumes sequential execution of
-        * the write-side. Add core synchronization instructions. Can be removed
-        * if the formal model is extended to prove that reordering is still
-        * correct.
+        * 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.
         */
-       sync_core();    /* Formal model assumes serialized execution */
+       smp_mb();
 
        /*
         * Wait for previous parity to be empty of readers.
@@ -269,7 +279,12 @@ void synchronize_rcu(void)
         * Ensured by STORE_SHARED and LOAD_SHARED.
         */
 
-       sync_core();    /* Formal model assumes serialized execution */
+       /*
+        * 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();
 
        switch_next_urcu_qparity();     /* 1 -> 0 */
 
@@ -281,7 +296,12 @@ void synchronize_rcu(void)
         * Ensured by STORE_SHARED and LOAD_SHARED.
         */
 
-       sync_core();    /* Formal model assumes serialized execution */
+       /*
+        * 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.
@@ -388,6 +408,7 @@ static void rcu_remove_reader(pthread_t id)
 void rcu_register_thread(void)
 {
        internal_urcu_lock();
+       urcu_init();    /* In case gcc does not support constructor attribute */
        rcu_add_reader(pthread_self());
        internal_urcu_unlock();
 }
@@ -412,12 +433,26 @@ static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
        smp_mb();
 }
 
-void __attribute__((constructor)) urcu_init(void)
+/*
+ * urcu_init constructor. Called when the library is linked, but also when
+ * reader threads are calling rcu_register_thread().
+ * Should only be called by a single thread at a given time. This is ensured by
+ * holing the internal_urcu_lock() from rcu_register_thread() or by running at
+ * library load time, which should not be executed by multiple threads nor
+ * concurrently with rcu_register_thread() anyway.
+ */
+void urcu_init(void)
 {
        struct sigaction act;
        int ret;
 
+       if (init_done)
+               return;
+       init_done = 1;
+
        act.sa_sigaction = sigurcu_handler;
+       act.sa_flags = SA_SIGINFO;
+       sigemptyset(&act.sa_mask);
        ret = sigaction(SIGURCU, &act, NULL);
        if (ret) {
                perror("Error in sigaction");
@@ -425,7 +460,7 @@ void __attribute__((constructor)) urcu_init(void)
        }
 }
 
-void __attribute__((destructor)) urcu_exit(void)
+void urcu_exit(void)
 {
        struct sigaction act;
        int ret;