call_rcu threads should clear their PAUSED flag when they unpause

And call_rcu_after_fork_parent should spin-wait on this.

Otherwise a second fork in the parent will see the PAUSED flags
already set and call_rcu_before_fork will not correctly wait for the
call_rcu threads to quiesce on this second occasion.

Fixes #786

Signed-off-by: Keir Fraser <keir@cohodata.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
index 10c4f3ec2fad83c61e8275059fc3ce7b618d4e5b..c2e175b7524982ab341f73865248404e8e303542 100644 (file)
--- a/urcu-call-rcu-impl.h
+++ b/urcu-call-rcu-impl.h
@@ -308,6 +308,8 @@ static void *call_rcu_thread(void *arg)
                        uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
                        while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
                                poll(NULL, 0, 1);
+                       uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
+                       cmm_smp_mb__after_uatomic_and();
                        rcu_register_thread();
                }
 
@@ -872,6 +874,10 @@ void call_rcu_after_fork_parent(void)
 
        cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
                uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
+       cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
+               while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
+                       poll(NULL, 0, 1);
+       }
        call_rcu_unlock(&call_rcu_mutex);
 }