Ensure LOAD_SHARED/STORE_SHARED semantic is used in QSBR RCU

[urcu.git] / urcu-qsbr.c

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index c0f055441930ab8718cd4d4347325bd6671dc2fc..e077eac8f2b4b4bc7c44cadaf0f96d012be60fe3 100644 (file)
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -32,6 +32,7 @@
 #include <errno.h>
 #include <poll.h>
 
+#define BUILD_QSBR_LIB
 #include "urcu-qsbr-static.h"
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu-qsbr.h"
@@ -114,9 +115,6 @@ static void wait_for_quiescent_state(void)
 {
        struct reader_registry *index;
 
-        if (rcu_reader_qs_gp & 1)
-            rcu_reader_qs_gp = urcu_gp_ctr + 1;
-
        if (!registry)
                return;
        /*
@@ -124,8 +122,7 @@ static void wait_for_quiescent_state(void)
         */
        for (index = registry; index < registry + num_readers; index++) {
 #ifndef HAS_INCOHERENT_CACHES
-               while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
-                      (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
+               while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
                        cpu_relax();
 #else /* #ifndef HAS_INCOHERENT_CACHES */
                int wait_loops = 0;
@@ -133,8 +130,7 @@ static void wait_for_quiescent_state(void)
                 * BUSY-LOOP. Force the reader thread to commit its
                 * rcu_reader_qs_gp update to memory if we wait for too long.
                 */
-               while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
-                      (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
+               while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
                        if (wait_loops++ == KICK_READER_LOOPS) {
                                force_mb_single_thread(index);
                                wait_loops = 0;
@@ -148,12 +144,27 @@ static void wait_for_quiescent_state(void)
 
 void synchronize_rcu(void)
 {
+       int was_online;
+
+       was_online = rcu_reader_qs_gp & 1;
+
+       /*
+        * Mark the writer thread offline to make sure we don't wait for
+        * our own quiescent state. This allows using synchronize_rcu() in
+        * threads registered as readers.
+        */
+       if (was_online)
+               _rcu_thread_offline();
+
        internal_urcu_lock();
        force_mb_all_threads();
-       urcu_gp_ctr += 2;
+       STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + 2);
        wait_for_quiescent_state();
        force_mb_all_threads();
        internal_urcu_unlock();
+
+       if (was_online)
+               _rcu_thread_online();
 }
 
 /*