[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PATCH v3 2/7] Implement drain_call_rcu and use it in hmp_device_del
From: |
Maxim Levitsky |
Subject: |
[PATCH v3 2/7] Implement drain_call_rcu and use it in hmp_device_del |
Date: |
Wed, 15 Jul 2020 18:01:54 +0300 |
This allows 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 <mlevitsk@redhat.com>
Suggested-by: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
include/qemu/rcu.h | 1 +
qdev-monitor.c | 22 +++++++++++++++++++
util/rcu.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 78 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/qdev-monitor.c b/qdev-monitor.c
index 71ebce19df..a889fbc509 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -803,6 +803,18 @@ void qmp_device_add(QDict *qdict, QObject **ret_data,
Error **errp)
return;
}
dev = qdev_device_add(opts, errp);
+
+ /*
+ * Drain all pending RCU callbacks. This is done because
+ * some bus related operations can delay a device removal
+ * (in this case this can happen if device is added and then
+ * removed due to a configuration error)
+ * to a RCU callback, but user might expect that this interface
+ * will finish its job completely once qmp command returns result
+ * to the user
+ */
+ drain_call_rcu();
+
if (!dev) {
qemu_opts_del(opts);
return;
@@ -894,6 +906,16 @@ void qmp_device_del(const char *id, Error **errp)
}
qdev_unplug(dev, errp);
+
+ /*
+ * Drain all pending RCU callbacks. This is done because
+ * some bus related operations can delay a device removal
+ * to a RCU callback, but user might expect that this interface
+ * will finish its job completely once qmp command returns result
+ * to the user
+ */
+
+ drain_call_rcu();
}
}
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);
--
2.26.2
- [PATCH v3 0/7] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread, Maxim Levitsky, 2020/07/15
- [PATCH v3 1/7] scsi/scsi_bus: switch search direction in scsi_device_find, Maxim Levitsky, 2020/07/15
- [PATCH v3 3/7] device-core: use RCU for list of childs of a bus, Maxim Levitsky, 2020/07/15
- [PATCH v3 4/7] device-core: use atomic_set on .realized property, Maxim Levitsky, 2020/07/15
- [PATCH v3 2/7] Implement drain_call_rcu and use it in hmp_device_del,
Maxim Levitsky <=
- [PATCH v3 5/7] virtio-scsi: don't touch scsi devices that are not yet realized or about to be un-realized, Maxim Levitsky, 2020/07/15
- [PATCH v3 7/7] virtio-scsi: use scsi_device_get, Maxim Levitsky, 2020/07/15
- [PATCH v3 6/7] scsi: Add scsi_device_get, Maxim Levitsky, 2020/07/15
- Re: [PATCH v3 0/7] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread, Maxim Levitsky, 2020/07/29