block: remove blk_needs_flush_plug

blk_needs_flush_plug fails to account for the cb_list, which needs
flushing as well.  Remove it and just check if there is a plug instead
of poking into the internals of the plug structure.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220127070549.1377856-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/fs-writeback.c

@@ -2301,7 +2301,7 @@ 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))
+	if (current->plug)
 		blk_flush_plug(current->plug, true);
 
 	rcu_read_lock();

include/linux/blkdev.h

@@ -1055,14 +1055,6 @@ extern void blk_finish_plug(struct blk_plug *);
 
 void blk_flush_plug(struct blk_plug *plug, bool from_schedule);
 
-static inline bool blk_needs_flush_plug(struct task_struct *tsk)
-{
-	struct blk_plug *plug = tsk->plug;
-
-	return plug &&
-		 (plug->mq_list || !list_empty(&plug->cb_list));
-}
-
 int blkdev_issue_flush(struct block_device *bdev);
 long nr_blockdev_pages(void);
 #else /* CONFIG_BLOCK */
@@ -1086,11 +1078,6 @@ static inline void blk_flush_plug(struct blk_plug *plug, bool async)
 {
 }
 
-static inline bool blk_needs_flush_plug(struct task_struct *tsk)
-{
-	return false;
-}
-
 static inline int blkdev_issue_flush(struct block_device *bdev)
 {
 	return 0;

kernel/exit.c

@@ -735,7 +735,7 @@ void __noreturn do_exit(long code)
 	struct task_struct *tsk = current;
 	int group_dead;
 
-	WARN_ON(blk_needs_flush_plug(tsk));
+	WARN_ON(tsk->plug);
 
 	/*
 	 * If do_dead is called because this processes oopsed, it's possible

kernel/sched/core.c

@@ -6344,7 +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 (blk_needs_flush_plug(tsk))
+	if (tsk->plug)
 		blk_flush_plug(tsk->plug, true);
 }