Add a mutex to allow possible creators of new work to synchronize with
flushing work queues.
Signed-off-by: NMike Anderson <andmike@linux.vnet.ibm.com>
Acked-by: NKiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>