mm/writeback: don't check force_wait to handle bdi->work_list

After commit 839a8e8660b6 ("writeback: replace custom worker pool
implementation with unbound workqueue"), bdi_writeback_workfn runs off
bdi_writeback->dwork, on each execution, it processes bdi->work_list and
reschedules if there are more things to do instead of flush any work
that race with us existing.  It is unecessary to check force_wait in
wb_do_writeback since it is always 0 after the mentioned commit.  This
patch remove the force_wait in wb_do_writeback.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fs-writeback.c

@@ -963,7 +963,7 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
 /*
  * Retrieve work items and do the writeback they describe
  */
-static long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
+static long wb_do_writeback(struct bdi_writeback *wb)
 {
 	struct backing_dev_info *bdi = wb->bdi;
 	struct wb_writeback_work *work;
@@ -971,12 +971,6 @@ static long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 
 	set_bit(BDI_writeback_running, &wb->bdi->state);
 	while ((work = get_next_work_item(bdi)) != NULL) {
-		/*
-		 * Override sync mode, in case we must wait for completion
-		 * because this thread is exiting now.
-		 */
-		if (force_wait)
-			work->sync_mode = WB_SYNC_ALL;
 
 		trace_writeback_exec(bdi, work);
 
@@ -1025,7 +1019,7 @@ void bdi_writeback_workfn(struct work_struct *work)
 		 * rescuer as work_list needs to be drained.
 		 */
 		do {
-			pages_written = wb_do_writeback(wb, 0);
+			pages_written = wb_do_writeback(wb);
 			trace_writeback_pages_written(pages_written);
 		} while (!list_empty(&bdi->work_list));
 	} else {