blk: clean up plug (dd6cf3e1) · Commits · 戴 / test

Current code looks like inner plug gets flushed with a blk_finish_plug(). Actually it's a nop. All requests/callbacks are added to current->plug, while only outmost plug is assigned to current->plug. So inner plug always has empty request/callback list, which makes blk_flush_plug_list() a nop. This tries to make the code more clear. Signed-off-by:

Shaohua Li <shli@fb.com> Reviewed-by:

Jeff Moyer <jmoyer@redhat.com> Reviewed-by:

Christoph Hellwig <hch@lst.de> Signed-off-by:

Jens Axboe <axboe@fb.com>

block/blk-core.c

+12 −12

Original line number	Diff line number	Diff line
		@@ -3032,22 +3032,21 @@ void blk_start_plug(struct blk_plug *plug)
		{
		struct task_struct *tsk = current;

		/*
		* If this is a nested plug, don't actually assign it.
		*/
		if (tsk->plug)
		return;

		INIT_LIST_HEAD(&plug->list);
		INIT_LIST_HEAD(&plug->mq_list);
		INIT_LIST_HEAD(&plug->cb_list);

		/*
		* If this is a nested plug, don't actually assign it. It will be
		* flushed on its own.
		*/
		if (!tsk->plug) {
		/*
		* Store ordering should not be needed here, since a potential
		* preempt will imply a full memory barrier
		*/
		tsk->plug = plug;
		}
		}
		EXPORT_SYMBOL(blk_start_plug);

		static int plug_rq_cmp(void priv, struct list_head a, struct list_head *b)
		@@ -3193,9 +3192,10 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)

		void blk_finish_plug(struct blk_plug *plug)
		{
		if (plug != current->plug)
		return;
		blk_flush_plug_list(plug, false);

		if (plug == current->plug)
		current->plug = NULL;
		}
		EXPORT_SYMBOL(blk_finish_plug);

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