Hi Dennis,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on block/for-next]
[also build test WARNING on v4.19-rc1 next-20180831]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Dennis-Zhou/blkcg-ref-count-refactor-cleanup-blkcg-avg_lat/20180831-161742
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: i386-randconfig-a1-201834 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.4-2) 4.9.4
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   In file included from include/linux/blkdev.h:21:0,
                    from drivers/usb//image/microtek.c:135:

quoted

include/linux/bio.h:566:17: warning: 'struct blkcg_gq' declared inside parameter list

             struct blkcg_gq *blkg) { return 0; }
                    ^

quoted

include/linux/bio.h:566:17: warning: its scope is only this definition or declaration, which is probably not what you want

vim +566 include/linux/bio.h

   555	
   556	#ifdef CONFIG_BLK_CGROUP
   557	int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
   558	int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg);
   559	int bio_associate_create_blkg(struct request_queue *q, struct bio *bio);
   560	void bio_disassociate_task(struct bio *bio);
   561	void bio_clone_blkcg_association(struct bio *dst, struct bio *src);
   562	#else	/* CONFIG_BLK_CGROUP */
   563	static inline int bio_associate_blkcg(struct bio *bio,
   564				struct cgroup_subsys_state *blkcg_css) { return 0; }
   565	static inline int bio_associate_blkg(struct bio *bio,
 > 566					     struct blkcg_gq *blkg) { return 0; }
   567	static inline int bio_associate_create_blkg(struct request_queue *q,
   568						    struct bio *bio) { return 0; }
   569	static inline void bio_disassociate_task(struct bio *bio) { }
   570	static inline void bio_clone_blkcg_association(struct bio *dst,
   571				struct bio *src) { }
   572	#endif	/* CONFIG_BLK_CGROUP */
   573	

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