This prevents a panic after a SLOG add/removal on the root pool followed
by a zpool scrub.
When a SLOG is removed, a hole takes its place - the vdev_ops for a hole
is vdev_hole_ops, which defines the handler functions of vdev_op_hold
and vdev_op_rele as NULL.
This bug has been reported in illumos and FreeBSD, a different trigger
in the FreeBSD report though.
Credit for this patch goes to Patrick Mooney <pmooney@pfmooney.com>
Obtained from: illumos-gate commit: c65bd18728f34725
External-issue: https://www.illumos.org/issues/12981
External-issue: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252396
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Wing <rob.fx907@gmail.com>
Closes#11623
11f2e9a491