block: cleanup the block plug helper functions

It's a bit of a mess currently. task->plug is being cleared
and reset in __blk_finish_plug(), and blk_finish_plug() is
testing for a NULL plug which cannot happen even from schedule()
anymore since it uses blk_needs_flush_plug() to determine
whether to call into this function at all.

So get rid of some of the cruft.
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/blk-core.c

@@ -2671,7 +2671,7 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth)
 		q->unplugged_fn(q);
 }
 
-static void flush_plug_list(struct blk_plug *plug)
+void blk_flush_plug_list(struct blk_plug *plug)
 {
 	struct request_queue *q;
 	unsigned long flags;
@@ -2733,28 +2733,16 @@ static void flush_plug_list(struct blk_plug *plug)
 
 	local_irq_restore(flags);
 }
-
-static void __blk_finish_plug(struct task_struct *tsk, struct blk_plug *plug)
-{
-	flush_plug_list(plug);
-
-	if (plug == tsk->plug)
-		tsk->plug = NULL;
-}
+EXPORT_SYMBOL(blk_flush_plug_list);
 
 void blk_finish_plug(struct blk_plug *plug)
 {
-	if (plug)
-		__blk_finish_plug(current, plug);
-}
-EXPORT_SYMBOL(blk_finish_plug);
+	blk_flush_plug_list(plug);
 
-void __blk_flush_plug(struct task_struct *tsk, struct blk_plug *plug)
-{
-	__blk_finish_plug(tsk, plug);
-	tsk->plug = plug;
+	if (plug == current->plug)
+		current->plug = NULL;
 }
-EXPORT_SYMBOL(__blk_flush_plug);
+EXPORT_SYMBOL(blk_finish_plug);
 
 int __init blk_dev_init(void)
 {

include/linux/blkdev.h

@@ -865,14 +865,14 @@ struct blk_plug {
 
 extern void blk_start_plug(struct blk_plug *);
 extern void blk_finish_plug(struct blk_plug *);
-extern void __blk_flush_plug(struct task_struct *, struct blk_plug *);
+extern void blk_flush_plug_list(struct blk_plug *);
 
 static inline void blk_flush_plug(struct task_struct *tsk)
 {
 	struct blk_plug *plug = tsk->plug;
 
-	if (unlikely(plug))
-		__blk_flush_plug(tsk, plug);
+	if (plug)
+		blk_flush_plug_list(plug);
 }
 
 static inline bool blk_needs_flush_plug(struct task_struct *tsk)