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[PULL 33/38] device-core: use atomic_set on .realized property
From: |
Paolo Bonzini |
Subject: |
[PULL 33/38] device-core: use atomic_set on .realized property |
Date: |
Mon, 12 Oct 2020 16:33:38 -0400 |
From: Maxim Levitsky <mlevitsk@redhat.com>
Some code might race with placement of new devices on a bus.
We currently first place a (unrealized) device on the bus
and then realize it.
As a workaround, users that scan the child device list, can
check the realized property to see if it is safe to access such a device.
Use an atomic write here too to aid with this.
A separate discussion is what to do with devices that are unrealized:
It looks like for this case we only call the hotplug handler's unplug
callback and its up to it to unrealize the device.
An atomic operation doesn't cause harm for this code path though.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200913160259.32145-6-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20201006123904.610658-10-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
hw/core/qdev.c | 19 ++++++++++++++++++-
include/hw/qdev-core.h | 2 ++
2 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 59e5e710b7..fc4daa36fa 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -946,7 +946,25 @@ static void device_set_realized(Object *obj, bool value,
Error **errp)
}
}
+ qatomic_store_release(&dev->realized, value);
+
} else if (!value && dev->realized) {
+
+ /*
+ * Change the value so that any concurrent users are aware
+ * that the device is going to be unrealized
+ *
+ * TODO: change .realized property to enum that states
+ * each phase of the device realization/unrealization
+ */
+
+ qatomic_set(&dev->realized, value);
+ /*
+ * Ensure that concurrent users see this update prior to
+ * any other changes done by unrealize.
+ */
+ smp_wmb();
+
QLIST_FOREACH(bus, &dev->child_bus, sibling) {
qbus_unrealize(bus);
}
@@ -961,7 +979,6 @@ static void device_set_realized(Object *obj, bool value,
Error **errp)
}
assert(local_err == NULL);
- dev->realized = value;
return;
child_realize_fail:
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 2c6307e3ed..868973319e 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -163,6 +163,8 @@ struct NamedClockList {
/**
* DeviceState:
* @realized: Indicates whether the device has been fully constructed.
+ * When accessed outsize big qemu lock, must be accessed with
+ * atomic_load_acquire()
* @reset: ResettableState for the device; handled by Resettable interface.
*
* This structure should not be accessed directly. We declare it here
--
2.26.2
- [PULL 22/38] qtest: Reintroduce qtest_qmp_receive with QMP event buffering, (continued)
- [PULL 22/38] qtest: Reintroduce qtest_qmp_receive with QMP event buffering, Paolo Bonzini, 2020/10/12
- [PULL 23/38] qtest: remove qtest_qmp_receive_success, Paolo Bonzini, 2020/10/12
- [PULL 19/38] build-sys: fix git version from -version, Paolo Bonzini, 2020/10/12
- [PULL 24/38] device-plug-test: use qtest_qmp to send the device_del command, Paolo Bonzini, 2020/10/12
- [PULL 25/38] qtest: switch users back to qtest_qmp_receive, Paolo Bonzini, 2020/10/12
- [PULL 20/38] meson.build: Re-enable KVM support for MIPS, Paolo Bonzini, 2020/10/12
- [PULL 21/38] qtest: rename qtest_qmp_receive to qtest_qmp_receive_dict, Paolo Bonzini, 2020/10/12
- [PULL 14/38] docs: Move QTest documentation to its own document, Paolo Bonzini, 2020/10/12
- [PULL 28/38] qdev: add "check if address free" callback for buses, Paolo Bonzini, 2020/10/12
- [PULL 16/38] docs/devel/qtest: Include libqtest API reference, Paolo Bonzini, 2020/10/12
- [PULL 33/38] device-core: use atomic_set on .realized property,
Paolo Bonzini <=
- [PULL 32/38] scsi: switch to bus->check_address, Paolo Bonzini, 2020/10/12
- [PULL 13/38] qom: fix objects with improper parent type, Paolo Bonzini, 2020/10/12
- [PULL 38/38] meson: identify more sections of meson.build, Paolo Bonzini, 2020/10/12
- [PULL 30/38] device_core: use drain_call_rcu in in qmp_device_add, Paolo Bonzini, 2020/10/12
- [PULL 37/38] scsi/scsi_bus: fix races in REPORT LUNS, Paolo Bonzini, 2020/10/12
- [PULL 34/38] scsi/scsi-bus: scsi_device_find: don't return unrealized devices, Paolo Bonzini, 2020/10/12
- [PULL 31/38] device-core: use RCU for list of children of a bus, Paolo Bonzini, 2020/10/12
- [PULL 36/38] virtio-scsi: use scsi_device_get, Paolo Bonzini, 2020/10/12