zil_claim_clone_range() takes references on cloned blocks before ZIL
replay. Later zil_free_clone_range() drops them after replay or on
dataset destroy. The total balance is neutral. It means on actual
replay we must take additional references, which would stay in BRT.
Without this blocks could be freed prematurely when either original
file or its clone are destroyed. I've observed BRT being emptied
and the feature being deactivated after ZIL replay completion, which
should not have happened. With the patch I see expected stats.
Reviewed-by: Kay Pedersen <mail@mkwg.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes#15603
a8c256046b