Hi Dennis,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on block/for-next]
[also build test ERROR 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: x86_64-randconfig-x019-201834 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   In file included from block/bio.c:20:0:
   include/linux/bio.h:565:17: warning: 'struct blkcg_gq' declared inside parameter list will not be visible outside of this definition or declaration
             struct blkcg_gq *blkg) { return 0; }
                    ^~~~~~~~
   block/bio.c: In function '__bio_clone_fast':
   block/bio.c:614:23: error: 'struct bio' has no member named 'bi_issue'; did you mean 'bi_disk'?
     bio_issue_init(&bio->bi_issue, bio_sectors(bio));
                          ^~~~~~~~
                          bi_disk
   block/bio.c: In function 'bio_endio':
>> block/bio.c:1750:11: error: 'struct bio' has no member named 'bi_blkg'; did you mean 'bi_flags'?
     if (bio->bi_blkg && bio->bi_blkg->parent)
              ^~~~~~~
              bi_flags
   block/bio.c:1750:27: error: 'struct bio' has no member named 'bi_blkg'; did you mean 'bi_flags'?
     if (bio->bi_blkg && bio->bi_blkg->parent)
                              ^~~~~~~
                              bi_flags

vim +1750 block/bio.c

  1727	
  1728	/**
  1729	 * bio_endio - end I/O on a bio
  1730	 * @bio:	bio
  1731	 *
  1732	 * Description:
  1733	 *   bio_endio() will end I/O on the whole bio. bio_endio() is the preferred
  1734	 *   way to end I/O on a bio. No one should call bi_end_io() directly on a
  1735	 *   bio unless they own it and thus know that it has an end_io function.
  1736	 *
  1737	 *   bio_endio() can be called several times on a bio that has been chained
  1738	 *   using bio_chain().  The ->bi_end_io() function will only be called the
  1739	 *   last time.  At this point the BLK_TA_COMPLETE tracing event will be
  1740	 *   generated if BIO_TRACE_COMPLETION is set.
  1741	 **/
  1742	void bio_endio(struct bio *bio)
  1743	{
  1744	again:
  1745		if (!bio_remaining_done(bio))
  1746			return;
  1747		if (!bio_integrity_endio(bio))
  1748			return;
  1749	
> 1750		if (bio->bi_blkg && bio->bi_blkg->parent)
  1751			blkg_record_latency(bio);
  1752	
  1753		if (bio->bi_disk)
  1754			rq_qos_done_bio(bio->bi_disk->queue, bio);
  1755	
  1756		/*
  1757		 * Need to have a real endio function for chained bios, otherwise
  1758		 * various corner cases will break (like stacking block devices that
  1759		 * save/restore bi_end_io) - however, we want to avoid unbounded
  1760		 * recursion and blowing the stack. Tail call optimization would
  1761		 * handle this, but compiling with frame pointers also disables
  1762		 * gcc's sibling call optimization.
  1763		 */
  1764		if (bio->bi_end_io == bio_chain_endio) {
  1765			bio = __bio_chain_endio(bio);
  1766			goto again;
  1767		}
  1768	
  1769		if (bio->bi_disk && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
  1770			trace_block_bio_complete(bio->bi_disk->queue, bio,
  1771						 blk_status_to_errno(bio->bi_status));
  1772			bio_clear_flag(bio, BIO_TRACE_COMPLETION);
  1773		}
  1774	
  1775		blk_throtl_bio_endio(bio);
  1776		/* release cgroup info */
  1777		bio_uninit(bio);
  1778		if (bio->bi_end_io)
  1779			bio->bi_end_io(bio);
  1780	}
  1781	EXPORT_SYMBOL(bio_endio);
  1782	

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