Re: [PATCH v5 0/7] vhost-user-blk: fix the migration issue and enhance qtests

[Dima Stepanov <dimastep@yandex-team.ru>]

On Thu, Sep 24, 2020 at 07:26:14AM -0400, Michael S. Tsirkin wrote:
> On Fri, Sep 11, 2020 at 11:39:42AM +0300, Dima Stepanov wrote:
> > v4 -> v5:
> >   - vhost: check queue state in the vhost_dev_set_log routine
> >     tests/qtest/vhost-user-test: prepare the tests for adding new
> >     dev class
> >     tests/qtest/vhost-user-test: add support for the
> >     vhost-user-blk device
> >     tests/qtest/vhost-user-test: add migrate_reconnect test
> >     Reviewed-by: Raphael Norwitz
> >   - Update qtest, by merging vhost-user-blk "if" case with the
> >     virtio-blk case.
> 
> I dropped patches 3-7 since they were stalling on some systems.
> Pls work with Peter Maydell (cc'd) to figure it out.
Thanks!

Peter, can you share any details for the stalling errors with me?

> 
> 
> > v3 -> v4:
> >   - vhost: recheck dev state in the vhost_migration_log routine
> >     Reviewed-by: Raphael Norwitz
> >   - vhost: check queue state in the vhost_dev_set_log routine
> >     Use "continue" instead of "break" to handle non-initialized
> >     virtqueue case.
> > 
> > v2 -> v3:
> >   - update commit message for the 
> >     "vhost: recheck dev state in the vhost_migration_log routine" commit
> >   - rename "started" field of the VhostUserBlk structure to
> >     "started_vu", so there will be no confustion with the VHOST started
> >     field
> >   - update vhost-user-test.c to always initialize nq local variable
> >     (spotted by patchew)
> > 
> > v1 -> v2:
> >   - add comments to connected/started fields in the header file
> >   - move the "s->started" logic from the vhost_user_blk_disconnect
> >     routine to the vhost_user_blk_stop routine
> > 
> > Reference e-mail threads:
> >   - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg01509.html
> >   - https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg05241.html
> > 
> > If vhost-user daemon is used as a backend for the vhost device, then we
> > should consider a possibility of disconnect at any moment. There was a general
> > question here: should we consider it as an error or okay state for the vhost-user
> > devices during migration process?
> > I think the disconnect event for the vhost-user devices 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
> > The first patch in the patchset fixes this issue by setting vhost device to the
> > stopped state in the disconnect handler and check it the vhost_migration_log()
> > routine before returning from the function.
> > qtest framework was updated to test vhost-user-blk functionality. The
> > vhost-user-blk/vhost-user-blk-tests/migrate_reconnect test was added to reproduce
> > the original issue found.
> > 
> > Dima Stepanov (7):
> >   vhost: recheck dev state in the vhost_migration_log routine
> >   vhost: check queue state in the vhost_dev_set_log routine
> >   tests/qtest/vhost-user-test: prepare the tests for adding new dev
> >     class
> >   tests/qtest/libqos/virtio-blk: add support for vhost-user-blk
> >   tests/qtest/vhost-user-test: add support for the vhost-user-blk device
> >   tests/qtest/vhost-user-test: add migrate_reconnect test
> >   tests/qtest/vhost-user-test: enable the reconnect tests
> > 
> >  hw/block/vhost-user-blk.c          |  19 ++-
> >  hw/virtio/vhost.c                  |  39 ++++-
> >  include/hw/virtio/vhost-user-blk.h |  10 ++
> >  tests/qtest/libqos/virtio-blk.c    |  14 +-
> >  tests/qtest/vhost-user-test.c      | 290 +++++++++++++++++++++++++++++++------
> >  5 files changed, 322 insertions(+), 50 deletions(-)
> > 
> > -- 
> > 2.7.4
>