[PULL 35/56] vhost-user-blk: delay vhost_user_blk_disconnect

[Michael S. Tsirkin]

From: Dima Stepanov <dimastep@yandex-team.ru>

A socket write during vhost-user communication may trigger a disconnect
event, calling vhost_user_blk_disconnect() and clearing all the
vhost_dev structures holding data that vhost-user functions expect to
remain valid to roll back initialization correctly. Delay the cleanup to
keep vhost_dev structure valid.
There are two possible states to handle:
1. RUN_STATE_PRELAUNCH: skip bh oneshot call and perform disconnect in
the caller routine.
2. RUN_STATE_RUNNING: delay by using bh

BH changes are based on the similar changes for the vhost-user-net
device:
  commit e7c83a885f865128ae3cf1946f8cb538b63cbfba
  "vhost-user: delay vhost_user_stop"

Signed-off-by: Dima Stepanov <dimastep@yandex-team.ru>
Message-Id: 
<69b73b94dcd066065595266c852810e0863a0895.1590396396.git.dimastep@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Li Feng <fengli@smartx.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
---
 hw/block/vhost-user-blk.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 9d8c0b3909..76838e76d3 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -349,6 +349,19 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
     vhost_dev_cleanup(&s->dev);
 }
 
+static void vhost_user_blk_event(void *opaque, QEMUChrEvent event);
+
+static void vhost_user_blk_chr_closed_bh(void *opaque)
+{
+    DeviceState *dev = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    vhost_user_blk_disconnect(dev);
+    qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
+            NULL, opaque, NULL, true);
+}
+
 static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
 {
     DeviceState *dev = opaque;
@@ -363,7 +376,30 @@ static void vhost_user_blk_event(void *opaque, 
QEMUChrEvent event)
         }
         break;
     case CHR_EVENT_CLOSED:
-        vhost_user_blk_disconnect(dev);
+        /*
+         * A close event may happen during a read/write, but vhost
+         * code assumes the vhost_dev remains setup, so delay the
+         * stop & clear. There are two possible paths to hit this
+         * disconnect event:
+         * 1. When VM is in the RUN_STATE_PRELAUNCH state. The
+         * vhost_user_blk_device_realize() is a caller.
+         * 2. In tha main loop phase after VM start.
+         *
+         * For p2 the disconnect event will be delayed. We can't
+         * do the same for p1, because we are not running the loop
+         * at this moment. So just skip this step and perform
+         * disconnect in the caller function.
+         *
+         * TODO: maybe it is a good idea to make the same fix
+         * for other vhost-user devices.
+         */
+        if (runstate_is_running()) {
+            AioContext *ctx = qemu_get_current_aio_context();
+
+            qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, NULL,
+                    NULL, NULL, false);
+            aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh, opaque);
+        }
         break;
     case CHR_EVENT_BREAK:
     case CHR_EVENT_MUX_IN:
-- 
MST