Fix 2 small bugs with cached dsl_scan_phys_t

This patch corrects 2 small bugs where scn->scn_phys_cached was
not properly updated to match the primary copy when it needed to
be. The first resulted in the pause state not being properly
updated and the second resulted in the cached version being
completely zeroed even if the primary was not.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Reviewed-by: Matthew Ahrens <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes openzfs#8010

module/zfs/dsl_scan.c

@@ -390,7 +390,6 @@ dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
 	scn->scn_maxinflight_bytes = MAX(zfs_scan_vdev_limit *
 	    dsl_scan_count_leaves(spa->spa_root_vdev), 1ULL << 20);
 
-	bcopy(&scn->scn_phys, &scn->scn_phys_cached, sizeof (scn->scn_phys));
 	avl_create(&scn->scn_queue, scan_ds_queue_compare, sizeof (scan_ds_t),
 	    offsetof(scan_ds_t, sds_node));
 	avl_create(&scn->scn_prefetch_queue, scan_prefetch_queue_compare,
@@ -484,6 +483,8 @@ dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
 		}
 	}
 
+	bcopy(&scn->scn_phys, &scn->scn_phys_cached, sizeof (scn->scn_phys));
+
 	/* reload the queue into the in-core state */
 	if (scn->scn_phys.scn_queue_obj != 0) {
 		zap_cursor_t zc;
@@ -969,6 +970,7 @@ dsl_scrub_pause_resume_sync(void *arg, dmu_tx_t *tx)
 		/* can't pause a scrub when there is no in-progress scrub */
 		spa->spa_scan_pass_scrub_pause = gethrestime_sec();
 		scn->scn_phys.scn_flags |= DSF_SCRUB_PAUSED;
+		scn->scn_phys_cached.scn_flags |= DSF_SCRUB_PAUSED;
 		dsl_scan_sync_state(scn, tx, SYNC_CACHED);
 		spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_PAUSED);
 	} else {
@@ -983,6 +985,7 @@ dsl_scrub_pause_resume_sync(void *arg, dmu_tx_t *tx)
 			    gethrestime_sec() - spa->spa_scan_pass_scrub_pause;
 			spa->spa_scan_pass_scrub_pause = 0;
 			scn->scn_phys.scn_flags &= ~DSF_SCRUB_PAUSED;
+			scn->scn_phys_cached.scn_flags &= ~DSF_SCRUB_PAUSED;
 			dsl_scan_sync_state(scn, tx, SYNC_CACHED);
 		}
 	}