When migration connection is broken, the QEMU and libvirtd(8)
process on the source side receive TCP connection reset
notification. QEMU sets the migration status to FAILED and
proceeds to migration_cleanup(). Meanwhile, Libvirtd(8) sends
a QMP command to migrate_set_capabilities().
The migration_cleanup() and qmp_migrate_set_capabilities()
calls race with each other. When the latter is invoked first,
since the migration is not running (FAILED), migration
capabilities are reset to false, so during migration_cleanup()
the QEMU process crashes with assertion failure.
Introduce a new migration status FAILING and use it as an
interim status when an error occurs. Once migration_cleanup()
is done, it sets the migration status to FAILED. This helps
to avoid the above race condition and ensuing failure.
Interim status FAILING is set wherever the execution moves
towards migration_cleanup():
- postcopy_start()
- migration_thread()
- migration_cleanup()
- multifd_send_setup()
- bg_migration_thread()
- migration_completion()
- migration_detect_error()
- bg_migration_completion()
- multifd_send_error_propagate()
- migration_connect_error_propagate()
The migration status finally moves to FAILED and reports an
appropriate error to the user.
Interim status FAILING is _NOT_ set in the following routines
because they do not follow the migration_cleanup() path to the
FAILED state:
- cpr_exec_cb()
- qemu_savevm_state()
- postcopy_listen_thread()
- process_incoming_migration_co()
- multifd_recv_terminate_threads()
- migration_channel_process_incoming()
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
Link: https://lore.kernel.org/qemu-devel/20260224102547.226087-1-ppandit@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
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