qemu/vhost-user-blk-delay-vhost_user_blk_disconnect.patch

From 632a841b6ba547906b475250f5c2cb46774ab4af Mon Sep 17 00:00:00 2001
From: Dima Stepanov <dimastep@yandex-team.ru>
Date: Thu, 28 May 2020 12:11:19 +0300
Subject: [PATCH 14/14] vhost-user-blk: delay vhost_user_blk_disconnect

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>
Signed-off-by: Peng Liang <liangpeng10@huawei.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 dc66f8a5febd..6b719d1d80e1 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -346,6 +346,19 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
     vhost_dev_cleanup(&s->dev);
 }
 
+static void vhost_user_blk_event(void *opaque, int 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, int event)
 {
     DeviceState *dev = opaque;
@@ -360,7 +373,30 @@ static void vhost_user_blk_event(void *opaque, int 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;
     }
 }
-- 
2.26.2