block: cleanup the flush plug helpers

Consolidate the various helpers into a single blk_flush_plug helper that
takes a plk_plug and the from_scheduler bool and switch all callsites to
call it directly.  Checks that the plug is non-NULL must be performed by
the caller, something that most already do anyway.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211020144119.142582-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 81ec192..4124a89 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1893,7 +1893,8 @@ static long writeback_sb_inodes(struct super_block *sb,
 			 * unplug, so get our IOs out the door before we
 			 * give up the CPU.
 			 */
-			blk_flush_plug(current);
+			if (current->plug)
+				blk_flush_plug(current->plug, false);
 			cond_resched();
 		}
 
@@ -2291,7 +2292,7 @@ void wakeup_flusher_threads(enum wb_reason reason)
 	 * If we are expecting writeback progress we must submit plugged IO.
 	 */
 	if (blk_needs_flush_plug(current))
-		blk_schedule_flush_plug(current);
+		blk_flush_plug(current->plug, true);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)