[Qemu-devel] [PULL 13/15] virtio-scsi: use aio handler for data plane

["Michael S. Tsirkin" <mst@redhat.com>]

From: Paolo Bonzini <pbonzini@redhat.com>

In addition to handling IO in vcpu thread and in io thread, dataplane
introduces yet another mode: handling it by AioContext.

This reuses the same handler as previous modes, which triggers races as
these were not designed to be reentrant.  Use a separate handler just
for aio, and disable regular handlers when dataplane is active.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/hw/virtio/virtio-scsi.h |  6 ++--
 hw/scsi/virtio-scsi-dataplane.c | 43 ++++++++++++++++++++++++---
 hw/scsi/virtio-scsi.c           | 65 ++++++++++++++++++++++++++++-------------
 3 files changed, 86 insertions(+), 28 deletions(-)

diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index eef4e95..ba2f5ce 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -139,9 +139,9 @@ void virtio_scsi_common_realize(DeviceState *dev, Error **errp,
                                 HandleOutput cmd);
 
 void virtio_scsi_common_unrealize(DeviceState *dev, Error **errp);
-void virtio_scsi_handle_ctrl_req(VirtIOSCSI *s, VirtIOSCSIReq *req);
-bool virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req);
-void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req);
+void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq);
+void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq);
+void virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq);
 void virtio_scsi_init_req(VirtIOSCSI *s, VirtQueue *vq, VirtIOSCSIReq *req);
 void virtio_scsi_free_req(VirtIOSCSIReq *req);
 void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice *dev,
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index b44ac5d..39ad086 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -38,7 +38,35 @@ void virtio_scsi_set_iothread(VirtIOSCSI *s, IOThread *iothread)
     }
 }
 
-static int virtio_scsi_vring_init(VirtIOSCSI *s, VirtQueue *vq, int n)
+static void virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
+                                              VirtQueue *vq)
+{
+    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
+
+    assert(s->ctx && s->dataplane_started);
+    virtio_scsi_handle_cmd_vq(s, vq);
+}
+
+static void virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
+                                               VirtQueue *vq)
+{
+    VirtIOSCSI *s = VIRTIO_SCSI(vdev);
+
+    assert(s->ctx && s->dataplane_started);
+    virtio_scsi_handle_ctrl_vq(s, vq);
+}
+
+static void virtio_scsi_data_plane_handle_event(VirtIODevice *vdev,
+                                                VirtQueue *vq)
+{
+    VirtIOSCSI *s = VIRTIO_SCSI(vdev);
+
+    assert(s->ctx && s->dataplane_started);
+    virtio_scsi_handle_event_vq(s, vq);
+}
+
+static int virtio_scsi_vring_init(VirtIOSCSI *s, VirtQueue *vq, int n,
+                                  void (*fn)(VirtIODevice *vdev, VirtQueue *vq))
 {
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
@@ -54,6 +82,7 @@ static int virtio_scsi_vring_init(VirtIOSCSI *s, VirtQueue *vq, int n)
     }
 
     virtio_queue_aio_set_host_notifier_handler(vq, s->ctx, true, true);
+    virtio_set_queue_aio(vq, fn);
     return 0;
 }
 
@@ -71,9 +100,12 @@ static void virtio_scsi_clear_aio(VirtIOSCSI *s)
     int i;
 
     virtio_queue_aio_set_host_notifier_handler(vs->ctrl_vq, s->ctx, false, false);
+    virtio_set_queue_aio(vs->ctrl_vq, NULL);
     virtio_queue_aio_set_host_notifier_handler(vs->event_vq, s->ctx, false, false);
+    virtio_set_queue_aio(vs->event_vq, NULL);
     for (i = 0; i < vs->conf.num_queues; i++) {
         virtio_queue_aio_set_host_notifier_handler(vs->cmd_vqs[i], s->ctx, false, false);
+        virtio_set_queue_aio(vs->cmd_vqs[i], NULL);
     }
 }
 
@@ -104,16 +136,19 @@ void virtio_scsi_dataplane_start(VirtIOSCSI *s)
     }
 
     aio_context_acquire(s->ctx);
-    rc = virtio_scsi_vring_init(s, vs->ctrl_vq, 0);
+    rc = virtio_scsi_vring_init(s, vs->ctrl_vq, 0,
+                                virtio_scsi_data_plane_handle_ctrl);
     if (rc) {
         goto fail_vrings;
     }
-    rc = virtio_scsi_vring_init(s, vs->event_vq, 1);
+    rc = virtio_scsi_vring_init(s, vs->event_vq, 1,
+                                virtio_scsi_data_plane_handle_event);
     if (rc) {
         goto fail_vrings;
     }
     for (i = 0; i < vs->conf.num_queues; i++) {
-        rc = virtio_scsi_vring_init(s, vs->cmd_vqs[i], i + 2);
+        rc = virtio_scsi_vring_init(s, vs->cmd_vqs[i], i + 2,
+                                    virtio_scsi_data_plane_handle_cmd);
         if (rc) {
             goto fail_vrings;
         }
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 38f1e2c..30415c6 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -374,7 +374,7 @@ fail:
     return ret;
 }
 
-void virtio_scsi_handle_ctrl_req(VirtIOSCSI *s, VirtIOSCSIReq *req)
+static void virtio_scsi_handle_ctrl_req(VirtIOSCSI *s, VirtIOSCSIReq *req)
 {
     VirtIODevice *vdev = (VirtIODevice *)s;
     uint32_t type;
@@ -412,20 +412,28 @@ void virtio_scsi_handle_ctrl_req(VirtIOSCSI *s, VirtIOSCSIReq *req)
     }
 }
 
-static void virtio_scsi_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
+void virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq)
 {
-    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
     VirtIOSCSIReq *req;
 
-    if (s->ctx && !s->dataplane_started) {
-        virtio_scsi_dataplane_start(s);
-        return;
-    }
     while ((req = virtio_scsi_pop_req(s, vq))) {
         virtio_scsi_handle_ctrl_req(s, req);
     }
 }
 
+static void virtio_scsi_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
+
+    if (s->ctx) {
+        virtio_scsi_dataplane_start(s);
+        if (!s->dataplane_fenced) {
+            return;
+        }
+    }
+    virtio_scsi_handle_ctrl_vq(s, vq);
+}
+
 static void virtio_scsi_complete_cmd_req(VirtIOSCSIReq *req)
 {
     /* Sense data is not in req->resp and is copied separately
@@ -508,7 +516,7 @@ static void virtio_scsi_fail_cmd_req(VirtIOSCSIReq *req)
     virtio_scsi_complete_cmd_req(req);
 }
 
-bool virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req)
+static bool virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req)
 {
     VirtIOSCSICommon *vs = &s->parent_obj;
     SCSIDevice *d;
@@ -550,7 +558,7 @@ bool virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req)
     return true;
 }
 
-void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
+static void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
 {
     SCSIRequest *sreq = req->sreq;
     if (scsi_req_enqueue(sreq)) {
@@ -560,17 +568,11 @@ void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
     scsi_req_unref(sreq);
 }
 
-static void virtio_scsi_handle_cmd(VirtIODevice *vdev, VirtQueue *vq)
+void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
 {
-    /* use non-QOM casts in the data path */
-    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
     VirtIOSCSIReq *req, *next;
     QTAILQ_HEAD(, VirtIOSCSIReq) reqs = QTAILQ_HEAD_INITIALIZER(reqs);
 
-    if (s->ctx && !s->dataplane_started) {
-        virtio_scsi_dataplane_start(s);
-        return;
-    }
     while ((req = virtio_scsi_pop_req(s, vq))) {
         if (virtio_scsi_handle_cmd_req_prepare(s, req)) {
             QTAILQ_INSERT_TAIL(&reqs, req, next);
@@ -582,6 +584,20 @@ static void virtio_scsi_handle_cmd(VirtIODevice *vdev, VirtQueue *vq)
     }
 }
 
+static void virtio_scsi_handle_cmd(VirtIODevice *vdev, VirtQueue *vq)
+{
+    /* use non-QOM casts in the data path */
+    VirtIOSCSI *s = (VirtIOSCSI *)vdev;
+
+    if (s->ctx) {
+        virtio_scsi_dataplane_start(s);
+        if (!s->dataplane_fenced) {
+            return;
+        }
+    }
+    virtio_scsi_handle_cmd_vq(s, vq);
+}
+
 static void virtio_scsi_get_config(VirtIODevice *vdev,
                                    uint8_t *config)
 {
@@ -725,17 +741,24 @@ out:
     }
 }
 
+void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq)
+{
+    if (s->events_dropped) {
+        virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
+    }
+}
+
 static void virtio_scsi_handle_event(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOSCSI *s = VIRTIO_SCSI(vdev);
 
-    if (s->ctx && !s->dataplane_started) {
+    if (s->ctx) {
         virtio_scsi_dataplane_start(s);
-        return;
-    }
-    if (s->events_dropped) {
-        virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
+        if (!s->dataplane_fenced) {
+            return;
+        }
     }
+    virtio_scsi_handle_event_vq(s, vq);
 }
 
 static void virtio_scsi_change(SCSIBus *bus, SCSIDevice *dev, SCSISense sense)
-- 
MST