virtio: Report real progress in VQ aio poll handler

In virtio_queue_host_notifier_aio_poll, not all "!virtio_queue_empty()"
cases are making true progress.

Currently the offending one is virtio-scsi event queue, whose handler
does nothing if no event is pending. As a result aio_poll() will spin on
the "non-empty" VQ and take 100% host CPU.

Fix this by reporting actual progress from virtio queue aio handlers.

Reported-by: Ed Swierk <eswierk@skyportsystems.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Tested-by: Ed Swierk <eswierk@skyportsystems.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

5 files changed, 39 insertions, 20 deletions

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index d1f9f63eaf..5556f0e64e 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -147,7 +147,7 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
     g_free(s);
 }
 
-static void virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
+static bool virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
                                                 VirtQueue *vq)
 {
     VirtIOBlock *s = (VirtIOBlock *)vdev;
@@ -155,7 +155,7 @@ static void virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
     assert(s->dataplane);
     assert(s->dataplane_started);
 
-    virtio_blk_handle_vq(s, vq);
+    return virtio_blk_handle_vq(s, vq);
 }
 
 /* Context: QEMU global mutex held */
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 702eda863e..baaa19593f 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -581,10 +581,11 @@ static int virtio_blk_handle_request(VirtIOBlockReq *req, MultiReqBuffer *mrb)
     return 0;
 }
 
-void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
+bool virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
 {
     VirtIOBlockReq *req;
     MultiReqBuffer mrb = {};
+    bool progress = false;
 
     blk_io_plug(s->blk);
 
@@ -592,6 +593,7 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
         virtio_queue_set_notification(vq, 0);
 
         while ((req = virtio_blk_get_request(s, vq))) {
+            progress = true;
             if (virtio_blk_handle_request(req, &mrb)) {
                 virtqueue_detach_element(req->vq, &req->elem, 0);
                 virtio_blk_free_request(req);
@@ -607,6 +609,12 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
     }
 
     blk_io_unplug(s->blk);
+    return progress;
+}
+
+static void virtio_blk_handle_output_do(VirtIOBlock *s, VirtQueue *vq)
+{
+    virtio_blk_handle_vq(s, vq);
 }
 
 static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
@@ -622,7 +630,7 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
             return;
         }
     }
-    virtio_blk_handle_vq(s, vq);
+    virtio_blk_handle_output_do(s, vq);
 }
 
 static void virtio_blk_dma_restart_bh(void *opaque)
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index 6b8d0f0024..74c95e0e60 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -49,35 +49,35 @@ void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error **errp)
     }
 }
 
-static void virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
+static bool 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);
+    return virtio_scsi_handle_cmd_vq(s, vq);
 }
 
-static void virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
+static bool 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);
+    return virtio_scsi_handle_ctrl_vq(s, vq);
 }
 
-static void virtio_scsi_data_plane_handle_event(VirtIODevice *vdev,
+static bool 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);
+    return 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))
+                                  VirtIOHandleAIOOutput fn)
 {
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
     int rc;
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index ce19efffc8..b01030b745 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -436,13 +436,16 @@ static inline void virtio_scsi_release(VirtIOSCSI *s)
     }
 }
 
-void virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq)
+bool virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq)
 {
     VirtIOSCSIReq *req;
+    bool progress = false;
 
     while ((req = virtio_scsi_pop_req(s, vq))) {
+        progress = true;
         virtio_scsi_handle_ctrl_req(s, req);
     }
+    return progress;
 }
 
 static void virtio_scsi_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
@@ -591,10 +594,11 @@ static void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
     scsi_req_unref(sreq);
 }
 
-void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
+bool virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
 {
     VirtIOSCSIReq *req, *next;
     int ret = 0;
+    bool progress = false;
 
     QTAILQ_HEAD(, VirtIOSCSIReq) reqs = QTAILQ_HEAD_INITIALIZER(reqs);
 
@@ -602,6 +606,7 @@ void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
         virtio_queue_set_notification(vq, 0);
 
         while ((req = virtio_scsi_pop_req(s, vq))) {
+            progress = true;
             ret = virtio_scsi_handle_cmd_req_prepare(s, req);
             if (!ret) {
                 QTAILQ_INSERT_TAIL(&reqs, req, next);
@@ -624,6 +629,7 @@ void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
     QTAILQ_FOREACH_SAFE(req, &reqs, next, next) {
         virtio_scsi_handle_cmd_req_submit(s, req);
     }
+    return progress;
 }
 
 static void virtio_scsi_handle_cmd(VirtIODevice *vdev, VirtQueue *vq)
@@ -752,11 +758,13 @@ out:
     virtio_scsi_release(s);
 }
 
-void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq)
+bool 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);
+        return true;
     }
+    return false;
 }
 
 static void virtio_scsi_handle_event(VirtIODevice *vdev, VirtQueue *vq)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 63657066e7..2461c06199 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -97,7 +97,7 @@ struct VirtQueue
 
     uint16_t vector;
     VirtIOHandleOutput handle_output;
-    VirtIOHandleOutput handle_aio_output;
+    VirtIOHandleAIOOutput handle_aio_output;
     VirtIODevice *vdev;
     EventNotifier guest_notifier;
     EventNotifier host_notifier;
@@ -1287,14 +1287,16 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align)
     virtio_queue_update_rings(vdev, n);
 }
 
-static void virtio_queue_notify_aio_vq(VirtQueue *vq)
+static bool virtio_queue_notify_aio_vq(VirtQueue *vq)
 {
     if (vq->vring.desc && vq->handle_aio_output) {
         VirtIODevice *vdev = vq->vdev;
 
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
-        vq->handle_aio_output(vdev, vq);
+        return vq->handle_aio_output(vdev, vq);
     }
+
+    return false;
 }
 
 static void virtio_queue_notify_vq(VirtQueue *vq)
@@ -2125,16 +2127,17 @@ static bool virtio_queue_host_notifier_aio_poll(void *opaque)
 {
     EventNotifier *n = opaque;
     VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
+    bool progress;
 
     if (virtio_queue_empty(vq)) {
         return false;
     }
 
-    virtio_queue_notify_aio_vq(vq);
+    progress = virtio_queue_notify_aio_vq(vq);
 
     /* In case the handler function re-enabled notifications */
     virtio_queue_set_notification(vq, 0);
-    return true;
+    return progress;
 }
 
 static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
@@ -2146,7 +2149,7 @@ static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
 }
 
 void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
-                                                VirtIOHandleOutput handle_output)
+                                                VirtIOHandleAIOOutput handle_output)
 {
     if (handle_output) {
         vq->handle_aio_output = handle_output;