block: check that there is a plug in blk_flush_plug

Rename blk_flush_plug to __blk_flush_plug and add a wrapper that includes
the NULL check instead of open coding that check everywhere.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220127070549.1377856-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -991,8 +991,7 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
 	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		return 0;
 
-	if (current->plug)
-		blk_flush_plug(current->plug, false);
+	blk_flush_plug(current->plug, false);
 
 	if (blk_queue_enter(q, BLK_MQ_REQ_NOWAIT))
 		return 0;
@@ -1274,7 +1273,7 @@ struct blk_plug_cb *blk_check_plugged(blk_plug_cb_fn unplug, void *data,
 }
 EXPORT_SYMBOL(blk_check_plugged);
 
-void blk_flush_plug(struct blk_plug *plug, bool from_schedule)
+void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
 {
 	if (!list_empty(&plug->cb_list))
 		flush_plug_callbacks(plug, from_schedule);
@@ -1303,7 +1302,7 @@ void blk_flush_plug(struct blk_plug *plug, bool from_schedule)
 void blk_finish_plug(struct blk_plug *plug)
 {
 	if (plug == current->plug) {
-		blk_flush_plug(plug, false);
+		__blk_flush_plug(plug, false);
 		current->plug = NULL;
 	}
 }

fs/fs-writeback.c

@@ -1903,8 +1903,7 @@ static long writeback_sb_inodes(struct super_block *sb,
 			 * unplug, so get our IOs out the door before we
 			 * give up the CPU.
 			 */
-			if (current->plug)
-				blk_flush_plug(current->plug, false);
+			blk_flush_plug(current->plug, false);
 			cond_resched();
 		}
 
@@ -2301,8 +2300,7 @@ void wakeup_flusher_threads(enum wb_reason reason)
 	/*
 	 * If we are expecting writeback progress we must submit plugged IO.
 	 */
-	if (current->plug)
-		blk_flush_plug(current->plug, true);
+	blk_flush_plug(current->plug, true);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)

include/linux/blkdev.h

@@ -1053,7 +1053,12 @@ extern void blk_start_plug(struct blk_plug *);
 extern void blk_start_plug_nr_ios(struct blk_plug *, unsigned short);
 extern void blk_finish_plug(struct blk_plug *);
 
-void blk_flush_plug(struct blk_plug *plug, bool from_schedule);
+void __blk_flush_plug(struct blk_plug *plug, bool from_schedule);
+static inline void blk_flush_plug(struct blk_plug *plug, bool async)
+{
+	if (plug)
+		__blk_flush_plug(plug, async);
+}
 
 int blkdev_issue_flush(struct block_device *bdev);
 long nr_blockdev_pages(void);

kernel/sched/core.c

@@ -6344,8 +6344,7 @@ static inline void sched_submit_work(struct task_struct *tsk)
 	 * If we are going to sleep and we have plugged IO queued,
 	 * make sure to submit it to avoid deadlocks.
 	 */
-	if (tsk->plug)
-		blk_flush_plug(tsk->plug, true);
+	blk_flush_plug(tsk->plug, true);
 }
 
 static void sched_update_worker(struct task_struct *tsk)
@@ -8371,9 +8370,7 @@ int io_schedule_prepare(void)
 	int old_iowait = current->in_iowait;
 
 	current->in_iowait = 1;
-	if (current->plug)
-		blk_flush_plug(current->plug, true);
-
+	blk_flush_plug(current->plug, true);
 	return old_iowait;
 }