From: Maxim Levitsky <mlevi...@redhat.com>
This will allow is to preserve the semantics of hmp_device_del,
that the device is deleted immediatly which was changed by previos
patch that delayed this to RCU callback
Signed-off-by: Maxim Levitsky <mlevi...@redhat.com>
Suggested-by: Stefan Hajnoczi <stefa...@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
---
include/qemu/rcu.h | 1 +
util/rcu.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 56 insertions(+)
diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index 570aa603eb..0e375ebe13 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -133,6 +133,7 @@ struct rcu_head {
};
extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
+extern void drain_call_rcu(void);
/* The operands of the minus operator must have the same type,
* which must be the one that we specify in the cast.
diff --git a/util/rcu.c b/util/rcu.c
index 60a37f72c3..c4fefa9333 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -293,6 +293,61 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct
rcu_head *node))
qemu_event_set(&rcu_call_ready_event);
}
+
+struct rcu_drain {
+ struct rcu_head rcu;
+ QemuEvent drain_complete_event;
+};
+
+static void drain_rcu_callback(struct rcu_head *node)
+{
+ struct rcu_drain *event = (struct rcu_drain *)node;
+ qemu_event_set(&event->drain_complete_event);
+}
+
+/*
+ * This function ensures that all pending RCU callbacks
+ * on the current thread are done executing
+
+ * drops big qemu lock during the wait to allow RCU thread
+ * to process the callbacks
+ *
+ */
+
+void drain_call_rcu(void)
+{
+ struct rcu_drain rcu_drain;
+ bool locked = qemu_mutex_iothread_locked();
+
+ memset(&rcu_drain, 0, sizeof(struct rcu_drain));
+ qemu_event_init(&rcu_drain.drain_complete_event, false);
+
+ if (locked) {
+ qemu_mutex_unlock_iothread();
+ }
+
+
+ /*
+ * RCU callbacks are invoked in the same order as in which they
+ * are registered, thus we can be sure that when 'drain_rcu_callback'
+ * is called, all RCU callbacks that were registered on this thread
+ * prior to calling this function are completed.
+ *
+ * Note that since we have only one global queue of the RCU callbacks,
+ * we also end up waiting for most of RCU callbacks that were registered
+ * on the other threads, but this is a side effect that shoudn't be
+ * assumed.
+ */
+
+ call_rcu1(&rcu_drain.rcu, drain_rcu_callback);
+ qemu_event_wait(&rcu_drain.drain_complete_event);
+
+ if (locked) {
+ qemu_mutex_lock_iothread();
+ }
+
+}
+
void rcu_register_thread(void)
{
assert(rcu_reader.ctr == 0);
--
2.28.0.windows.1
