Fix txg_sync_thread hang in scan_exec_io()

When scn->scn_maxinflight_bytes has not been initialized it's
possible to hang on the condition variable in scan_exec_io().
This issue was uncovered by ztest and is only possible when
deduplication is enabled through the following call path.

  txg_sync_thread()
    spa_sync()
      ddt_sync_table()
        ddt_sync_entry()
          dsl_scan_ddt_entry()
            dsl_scan_scrub_cb()
              dsl_scan_enqueuei()
                scan_exec_io()
                  cv_wait()

Resolve the issue by always initializing scn_maxinflight_bytes
to a reasonable minimum value.  This value will be recalculated
in dsl_scan_sync() to pick up changes to zfs_scan_vdev_limit
and the addition/removal of vdevs.

Reviewed-by: Tom Caputi <[email protected]>
Reviewed by: George Melikov <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #7098 

0 files changed, 0 insertions, 0 deletions