The zpool reguid feature introduced the spa_load_guid, which is a
transient value used for runtime identification purposes in the ARC.
This value is not the same as the spa's persistent pool guid.
However, the value is seeded from spa_generate_load_guid() which
does not check for uniqueness against the spa_load_guid from other
pools. Although extremely rare, you can end up with two different
pools sharing the same spa_load_guid value!
This change guarantees that the value is always unique and
additionally not still in use by an async arc flush task.
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Don Brady <don.brady@klarasystems.com>
52b68cd342