virtio: make it possible to detach host notifier from any thread

virtio_queue_aio_detach_host_notifier() does two things:
1. It removes the fd handler from the event loop.
2. It processes the virtqueue one last time.

The first step can be peformed by any thread and without taking the
AioContext lock.

The second step may need the AioContext lock (depending on the device
implementation) and runs in the thread where request processing takes
place. virtio-blk and virtio-scsi therefore call
virtio_queue_aio_detach_host_notifier() from a BH that is scheduled in
AioContext.

The next patch will introduce a .drained_begin() function that needs to
call virtio_queue_aio_detach_host_notifier(). .drained_begin() functions
cannot call aio_poll() to wait synchronously for the BH. It is possible
for a .drained_poll() callback to asynchronously wait for the BH, but
that is more complex than necessary here.

Move the virtqueue processing out to the callers of
virtio_queue_aio_detach_host_notifier() so that the function can be
called from any thread. This is in preparation for the next patch.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230516190238.8401-17-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index af1c24c40c1f2ca61b3f29bf3067222d5d42f05e..4f5c7cd55fe20e4be25a590b1ac4746a8508c82c 100644 (file)
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -287,8 +287,15 @@ static void virtio_blk_data_plane_stop_bh(void *opaque)
 
     for (i = 0; i < s->conf->num_queues; i++) {
         VirtQueue *vq = virtio_get_queue(s->vdev, i);
+        EventNotifier *host_notifier = virtio_queue_get_host_notifier(vq);
 
         virtio_queue_aio_detach_host_notifier(vq, s->ctx);
+
+        /*
+         * Test and clear notifier after disabling event, in case poll callback
+         * didn't have time to run.
+         */
+        virtio_queue_host_notifier_read(host_notifier);
     }
 }
 

diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index f3214e1c57e52a5c535641acc4e73e263216b5fd..b3a1ed21f7d4dd9f968e0a7f5e90752e5be986da 100644 (file)
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -71,12 +71,26 @@ static void virtio_scsi_dataplane_stop_bh(void *opaque)
 {
     VirtIOSCSI *s = opaque;
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
+    EventNotifier *host_notifier;
     int i;
 
     virtio_queue_aio_detach_host_notifier(vs->ctrl_vq, s->ctx);
+    host_notifier = virtio_queue_get_host_notifier(vs->ctrl_vq);
+
+    /*
+     * Test and clear notifier after disabling event, in case poll callback
+     * didn't have time to run.
+     */
+    virtio_queue_host_notifier_read(host_notifier);
+
     virtio_queue_aio_detach_host_notifier(vs->event_vq, s->ctx);
+    host_notifier = virtio_queue_get_host_notifier(vs->event_vq);
+    virtio_queue_host_notifier_read(host_notifier);
+
     for (i = 0; i < vs->conf.num_queues; i++) {
         virtio_queue_aio_detach_host_notifier(vs->cmd_vqs[i], s->ctx);
+        host_notifier = virtio_queue_get_host_notifier(vs->cmd_vqs[i]);
+        virtio_queue_host_notifier_read(host_notifier);
     }
 }
 

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 272d93072122980ca6cb490423bdb8fe86d44686..cb09cb64640cddfc70f8700c7ee61575230bf5d1 100644 (file)
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3516,9 +3516,6 @@ void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioContext *ct
 void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx)
 {
     aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL, NULL, NULL);
-    /* Test and clear notifier before after disabling event,
-     * in case poll callback didn't have time to run. */
-    virtio_queue_host_notifier_read(&vq->host_notifier);
 }
 
 void virtio_queue_host_notifier_read(EventNotifier *n)