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virtio-scsi: replace AioContext lock with tmf_bh_lock

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Protect the Task Management Function BH state with a lock. The TMF BH
runs in the main loop thread. An IOThread might process a TMF at the
same time as the TMF BH is running. Therefore tmf_bh_list and tmf_bh
must be protected by a lock.

Run TMF request completion in the IOThread using aio_wait_bh_oneshot().
This avoids more locking to protect the virtqueue and SCSI layer state.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231205182011.1976568-2-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-12-05 13:19:58 -05:00 committed by Kevin Wolf
parent e661a24703
commit ed18b1ed4f
2 changed files with 43 additions and 22 deletions
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62
hw/scsi/virtio-scsi.c
View File

@ -123,6 +123,30 @@ static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
virtio_scsi_free_req(req);
}
static void virtio_scsi_complete_req_bh(void *opaque)
{
VirtIOSCSIReq *req = opaque;
virtio_scsi_complete_req(req);
}
/*
* Called from virtio_scsi_do_one_tmf_bh() in main loop thread. The main loop
* thread cannot touch the virtqueue since that could race with an IOThread.
*/
static void virtio_scsi_complete_req_from_main_loop(VirtIOSCSIReq *req)
{
VirtIOSCSI *s = req->dev;
if (!s->ctx || s->ctx == qemu_get_aio_context()) {
/* No need to schedule a BH when there is no IOThread */
virtio_scsi_complete_req(req);
} else {
/* Run request completion in the IOThread */
aio_wait_bh_oneshot(s->ctx, virtio_scsi_complete_req_bh, req);
}
}
static void virtio_scsi_bad_req(VirtIOSCSIReq *req)
{
virtio_error(VIRTIO_DEVICE(req->dev), "wrong size for virtio-scsi headers");
@ -338,10 +362,7 @@ static void virtio_scsi_do_one_tmf_bh(VirtIOSCSIReq *req)
out:
object_unref(OBJECT(d));
virtio_scsi_acquire(s);
virtio_scsi_complete_req(req);
virtio_scsi_release(s);
virtio_scsi_complete_req_from_main_loop(req);
}
/* Some TMFs must be processed from the main loop thread */
@ -354,18 +375,16 @@ static void virtio_scsi_do_tmf_bh(void *opaque)
GLOBAL_STATE_CODE();
virtio_scsi_acquire(s);
WITH_QEMU_LOCK_GUARD(&s->tmf_bh_lock) {
QTAILQ_FOREACH_SAFE(req, &s->tmf_bh_list, next, tmp) {
QTAILQ_REMOVE(&s->tmf_bh_list, req, next);
QTAILQ_INSERT_TAIL(&reqs, req, next);
}
QTAILQ_FOREACH_SAFE(req, &s->tmf_bh_list, next, tmp) {
QTAILQ_REMOVE(&s->tmf_bh_list, req, next);
QTAILQ_INSERT_TAIL(&reqs, req, next);
qemu_bh_delete(s->tmf_bh);
s->tmf_bh = NULL;
}
qemu_bh_delete(s->tmf_bh);
s->tmf_bh = NULL;
virtio_scsi_release(s);
QTAILQ_FOREACH_SAFE(req, &reqs, next, tmp) {
QTAILQ_REMOVE(&reqs, req, next);
virtio_scsi_do_one_tmf_bh(req);
@ -379,8 +398,7 @@ static void virtio_scsi_reset_tmf_bh(VirtIOSCSI *s)
GLOBAL_STATE_CODE();
virtio_scsi_acquire(s);
/* Called after ioeventfd has been stopped, so tmf_bh_lock is not needed */
if (s->tmf_bh) {
qemu_bh_delete(s->tmf_bh);
s->tmf_bh = NULL;
@ -393,19 +411,19 @@ static void virtio_scsi_reset_tmf_bh(VirtIOSCSI *s)
req->resp.tmf.response = VIRTIO_SCSI_S_TARGET_FAILURE;
virtio_scsi_complete_req(req);
}
virtio_scsi_release(s);
}
static void virtio_scsi_defer_tmf_to_bh(VirtIOSCSIReq *req)
{
VirtIOSCSI *s = req->dev;
QTAILQ_INSERT_TAIL(&s->tmf_bh_list, req, next);
WITH_QEMU_LOCK_GUARD(&s->tmf_bh_lock) {
QTAILQ_INSERT_TAIL(&s->tmf_bh_list, req, next);
if (!s->tmf_bh) {
s->tmf_bh = qemu_bh_new(virtio_scsi_do_tmf_bh, s);
qemu_bh_schedule(s->tmf_bh);
if (!s->tmf_bh) {
s->tmf_bh = qemu_bh_new(virtio_scsi_do_tmf_bh, s);
qemu_bh_schedule(s->tmf_bh);
}
}
}
@ -1235,6 +1253,7 @@ static void virtio_scsi_device_realize(DeviceState *dev, Error **errp)
Error *err = NULL;
QTAILQ_INIT(&s->tmf_bh_list);
qemu_mutex_init(&s->tmf_bh_lock);
virtio_scsi_common_realize(dev,
virtio_scsi_handle_ctrl,
@ -1277,6 +1296,7 @@ static void virtio_scsi_device_unrealize(DeviceState *dev)
qbus_set_hotplug_handler(BUS(&s->bus), NULL);
virtio_scsi_common_unrealize(dev);
qemu_mutex_destroy(&s->tmf_bh_lock);
}
static Property virtio_scsi_properties[] = {

3
include/hw/virtio/virtio-scsi.h
View File

@ -85,8 +85,9 @@ struct VirtIOSCSI {
/*
* TMFs deferred to main loop BH. These fields are protected by
* virtio_scsi_acquire().
* tmf_bh_lock.
*/
QemuMutex tmf_bh_lock;
QEMUBH *tmf_bh;
QTAILQ_HEAD(, VirtIOSCSIReq) tmf_bh_list;