scsi: qla2xxx: Always wait for qlt_sess_work_fn() from qlt_stop_phase1()

Currently qlt_stop_phase1() may fail to call flush_scheduled_work(), for
list_empty() may return true as soon as qlt_sess_work_fn() called
list_del(). In order to close this race window, check list_empty() after
calling flush_scheduled_work().

If this patch causes problems, please check commit c4f135d6
("workqueue: Wrap flush_workqueue() using a macro"). We are on the way to
remove all flush_scheduled_work() calls from the kernel.

Link: https://lore.kernel.org/r/7f24469d-9e39-3398-d851-329b54c0b923@I-love.SAKURA.ne.jpTested-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qla2xxx/qla_target.c

@@ -1557,11 +1557,11 @@ int qlt_stop_phase1(struct qla_tgt *tgt)
 	ql_dbg(ql_dbg_tgt_mgt, vha, 0xf009,
 	    "Waiting for sess works (tgt %p)", tgt);
 	spin_lock_irqsave(&tgt->sess_work_lock, flags);
-	while (!list_empty(&tgt->sess_works_list)) {
+	do {
 		spin_unlock_irqrestore(&tgt->sess_work_lock, flags);
 		flush_scheduled_work();
 		spin_lock_irqsave(&tgt->sess_work_lock, flags);
-	}
+	} while (!list_empty(&tgt->sess_works_list));
 	spin_unlock_irqrestore(&tgt->sess_work_lock, flags);
 
 	ql_dbg(ql_dbg_tgt_mgt, vha, 0xf00a,