QSBR: add missing wakeups in synchronize_rcu code

synchronize_rcu go into offline mode during grace period. It duplicates
the rcu_thread_online/offline code, and therefore adding the required
wake_up_gp() is required there too.

Failure to do so leads to grace period hangs.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 5e4348449ca9183b61bf1cbc6a041a549f784c2b..1dc99792d7a49f2f6f3614693e34cde239312bfb 100644 (file)
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -218,8 +218,11 @@ void synchronize_rcu(void)
         * our own quiescent state. This allows using synchronize_rcu()
         * in threads registered as readers.
         */
-       if (was_online)
+       if (was_online) {
                CMM_STORE_SHARED(rcu_reader.ctr, 0);
+               cmm_smp_mb();   /* write rcu_reader.ctr before read futex */
+               wake_up_gp();
+       }
 
        mutex_lock(&rcu_gp_lock);
 
@@ -277,8 +280,11 @@ void synchronize_rcu(void)
         * in threads registered as readers.
         */
        cmm_smp_mb();
-       if (was_online)
+       if (was_online) {
                CMM_STORE_SHARED(rcu_reader.ctr, 0);
+               cmm_smp_mb();   /* write rcu_reader.ctr before read futex */
+               wake_up_gp();
+       }
 
        mutex_lock(&rcu_gp_lock);
        if (cds_list_empty(&registry))