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Re: [PATCH v4 1/7] vhost: recheck dev state in the vhost_migration_log r
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH v4 1/7] vhost: recheck dev state in the vhost_migration_log routine |
Date: |
Tue, 8 Sep 2020 15:25:20 +0100 |
On Fri, Sep 04, 2020 at 12:31:13PM +0300, Dima Stepanov wrote:
> vhost-user devices can get a disconnect in the middle of the VHOST-USER
> handshake on the migration start. If disconnect event happened right
> before sending next VHOST-USER command, then the vhost_dev_set_log()
> call in the vhost_migration_log() function will return error. This error
> will lead to the assert() and close the QEMU migration source process.
> For the vhost-user devices the disconnect event should not break the
> migration process, because:
> - the device will be in the stopped state, so it will not be changed
> during migration
> - if reconnect will be made the migration log will be reinitialized as
> part of reconnect/init process:
> #0 vhost_log_global_start (listener=0x563989cf7be0)
> at hw/virtio/vhost.c:920
> #1 0x000056398603d8bc in listener_add_address_space
> (listener=0x563989cf7be0,
> as=0x563986ea4340 <address_space_memory>)
> at softmmu/memory.c:2664
> #2 0x000056398603dd30 in memory_listener_register
> (listener=0x563989cf7be0,
> as=0x563986ea4340 <address_space_memory>)
> at softmmu/memory.c:2740
> #3 0x0000563985fd6956 in vhost_dev_init (hdev=0x563989cf7bd8,
> opaque=0x563989cf7e30, backend_type=VHOST_BACKEND_TYPE_USER,
> busyloop_timeout=0)
> at hw/virtio/vhost.c:1385
> #4 0x0000563985f7d0b8 in vhost_user_blk_connect (dev=0x563989cf7990)
> at hw/block/vhost-user-blk.c:315
> #5 0x0000563985f7d3f6 in vhost_user_blk_event (opaque=0x563989cf7990,
> event=CHR_EVENT_OPENED)
> at hw/block/vhost-user-blk.c:379
> Update the vhost-user-blk device with the internal started_vu field which
> will be used for initialization (vhost_user_blk_start) and clean up
> (vhost_user_blk_stop). This additional flag in the VhostUserBlk structure
> will be used to track whether the device really needs to be stopped and
> cleaned up on a vhost-user level.
> The disconnect event will set the overall VHOST device (not vhost-user) to
> the stopped state, so it can be used by the general vhost_migration_log
> routine.
> Such approach could be propogated to the other vhost-user devices, but
> better idea is just to make the same connect/disconnect code for all the
> vhost-user devices.
>
> This migration issue was slightly discussed earlier:
> - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg01509.html
> - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg05241.html
>
> Signed-off-by: Dima Stepanov <dimastep@yandex-team.ru>
> Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> ---
> hw/block/vhost-user-blk.c | 19 ++++++++++++++++---
> hw/virtio/vhost.c | 27 ++++++++++++++++++++++++---
> include/hw/virtio/vhost-user-blk.h | 10 ++++++++++
> 3 files changed, 50 insertions(+), 6 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 39aec42..a076b1e 100644
> --- a/hw/block/vhost-user-blk.c
> +++ b/hw/block/vhost-user-blk.c
> @@ -150,6 +150,7 @@ static int vhost_user_blk_start(VirtIODevice *vdev)
> error_report("Error starting vhost: %d", -ret);
> goto err_guest_notifiers;
> }
> + s->started_vu = true;
>
> /* guest_notifier_mask/pending not used yet, so just unmask
> * everything here. virtio-pci will do the right thing by
> @@ -175,6 +176,11 @@ static void vhost_user_blk_stop(VirtIODevice *vdev)
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> int ret;
>
> + if (!s->started_vu) {
> + return;
> + }
> + s->started_vu = false;
> +
> if (!k->set_guest_notifiers) {
> return;
> }
> @@ -341,9 +347,7 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
> }
> s->connected = false;
>
> - if (s->dev.started) {
> - vhost_user_blk_stop(vdev);
> - }
> + vhost_user_blk_stop(vdev);
>
> vhost_dev_cleanup(&s->dev);
> }
> @@ -399,6 +403,15 @@ static void vhost_user_blk_event(void *opaque,
> QEMUChrEvent event)
> NULL, NULL, false);
> aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh,
> opaque);
> }
> +
> + /*
> + * Move vhost device to the stopped state. The vhost-user device
> + * will be clean up and disconnected in BH. This can be useful in
> + * the vhost migration code. If disconnect was caught there is an
> + * option for the general vhost code to get the dev state without
> + * knowing its type (in this case vhost-user).
> + */
> + s->dev.started = false;
> break;
> case CHR_EVENT_BREAK:
> case CHR_EVENT_MUX_IN:
Hi Dima,
Is it possible to move this logic into the vhost_*() API so that all
devices benefit from it? This seems like a generic vhost-user issue
rather than a vhost-user-blk issue.
In other words, it would be great if the vhost APIs in QEMU are designed
in a way so that the user doesn't need to think about this.
Stefan
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- [PATCH v4 0/7] vhost-user-blk: fix the migration issue and enhance qtests, Dima Stepanov, 2020/09/04
- [PATCH v4 2/7] vhost: check queue state in the vhost_dev_set_log routine, Dima Stepanov, 2020/09/04
- [PATCH v4 1/7] vhost: recheck dev state in the vhost_migration_log routine, Dima Stepanov, 2020/09/04
- Re: [PATCH v4 1/7] vhost: recheck dev state in the vhost_migration_log routine,
Stefan Hajnoczi <=
- [PATCH v4 3/7] tests/qtest/vhost-user-test: prepare the tests for adding new dev class, Dima Stepanov, 2020/09/04
- [PATCH v4 5/7] tests/qtest/vhost-user-test: add support for the vhost-user-blk device, Dima Stepanov, 2020/09/04
- [PATCH v4 7/7] tests/qtest/vhost-user-test: enable the reconnect tests, Dima Stepanov, 2020/09/04
- [PATCH v4 6/7] tests/qtest/vhost-user-test: add migrate_reconnect test, Dima Stepanov, 2020/09/04