This patch is part of an effort to remove the aio_disable_external()
API because it does not fit in a multi-queue block layer world where
many AioContexts may be submitting requests to the same disk.
The SCSI emulation code is already in good shape to stop using
aio_disable_external(). It was only used by commit 9c5aad84da1c
("virtio-scsi: fixed virtio_scsi_ctx_check failed when detaching scsi
disk") to ensure that virtio_scsi_hotunplug() works while the guest
driver is submitting I/O.
Ensure virtio_scsi_hotunplug() is safe as follows:
1. qdev_simple_device_unplug_cb() -> qdev_unrealize() ->
device_set_realized() calls qatomic_set(&dev->realized, false) so
that future scsi_device_get() calls return NULL because they exclude
SCSIDevices with realized=false.
That means virtio-scsi will reject new I/O requests to this
SCSIDevice with VIRTIO_SCSI_S_BAD_TARGET even while
virtio_scsi_hotunplug() is still executing. We are protected against
new requests!
2. Add a call to scsi_device_purge_requests() from scsi_unrealize() so
that in-flight requests are cancelled synchronously. This ensures
that no in-flight requests remain once qdev_simple_device_unplug_cb()
returns.
Thanks to these two conditions we don't need aio_disable_external()
anymore.
Cc: Zhengui Li <lizhengui@huawei.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
hw/scsi/scsi-disk.c | 1 +
hw/scsi/virtio-scsi.c | 3 ---
2 files changed, 1 insertion(+), 3 deletions(-)
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 97c9b1c8cd..e01bd84541 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2522,6 +2522,7 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
static void scsi_unrealize(SCSIDevice *dev)
{
+ scsi_device_purge_requests(dev, SENSE_CODE(RESET));
del_boot_device_lchs(&dev->qdev, NULL);
}
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 000961446c..a02f9233ec 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -1061,11 +1061,8 @@ static void virtio_scsi_hotunplug(HotplugHandler
*hotplug_dev, DeviceState *dev,
VirtIODevice *vdev = VIRTIO_DEVICE(hotplug_dev);
VirtIOSCSI *s = VIRTIO_SCSI(vdev);
SCSIDevice *sd = SCSI_DEVICE(dev);
- AioContext *ctx = s->ctx ?: qemu_get_aio_context();
- aio_disable_external(ctx);
qdev_simple_device_unplug_cb(hotplug_dev, dev, errp);
- aio_enable_external(ctx);
if (s->ctx) {
virtio_scsi_acquire(s);