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Re: [PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect
From: |
Dima Stepanov |
Subject: |
Re: [PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect |
Date: |
Mon, 25 May 2020 11:57:49 +0300 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, May 20, 2020 at 06:53:13PM +0300, Dima Stepanov wrote:
> 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 <address@hidden>
I've reworked the patch based on Raphael's comment and send it for
review. Also i added a TODO comment in the vhost_user_blk_event()
routine. After review i'll send a v4 patch set.
---
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 9d8c0b3..76838e7 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:
--
2.7.4