Re: [PATCH v2 2/5] migration/postcopy: set destination postcopy-active in the run BH

[Eric Blake <eblake@redhat.com>]

On Tue, Nov 10, 2026 at 07:32:54PM +0100, Denis V. Lunev wrote:
> From: Denis V. Lunev <den@openvz.org>
> 
> Commit 7b842fe354c ("migration: Introduce POSTCOPY_DEVICE state") made
> the destination enter POSTCOPY_ACTIVE in loadvm_postcopy_handle_run(),
> before it schedules loadvm_postcopy_handle_run_bh(), and only the BH
> starts the VM or moves it to RUN_STATE_PAUSED. Management reacting to
> the destination's postcopy-active event can therefore still find the
> VM in RUN_STATE_INMIGRATE, where blockdev-add creates inactive nodes
> and attaching a device to them fails with "Block node is read-only".
> 
> Move the transition to the end of the run BH, after vm_start() or
> runstate_set(), as process_incoming_migration_bh() does for precopy
> COMPLETED. Without a return path the listen thread enters
> POSTCOPY_ACTIVE directly, and the fast snapshot load path switches
> right after scheduling the BH; in both cases the state is no longer
> POSTCOPY_DEVICE when the BH runs and the transition is a no-op.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Fabiano Rosas <farosas@suse.de>
> Cc: Juraj Marcin <jmarcin@redhat.com>
> ---
>  migration/savevm.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)

I'll defer to Peter's judgment on this one and 4/5, but the
descriptions in the cover letter and commit message make sense to
me. Meanwhile, I'm setting up to play with 3 and 5/5 to see if I can
review those tests for catching the issues documented here, even if
I'm less comfortable being the sole reviewer on the code changes that
got them to pass.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org