blkcg: use the usual get blkg path for root blkio_group

For root blkg, blk_throtl_init() was using throtl_alloc_tg()
explicitly and cfq_init_queue() was manually initializing embedded
cfqd->root_group, adding unnecessarily different code paths to blkg
handling.

Make both use the usual blkio_group get functions - throtl_get_tg()
and cfq_get_cfqg() - for the root blkio_group too.  Note that
blk_throtl_init() callsite is pushed downwards in
blk_alloc_queue_node() so that @q is sufficiently initialized for
throtl_get_tg().

This simplifies root blkg handling noticeably for cfq and will allow
further modularization of blkcg API.

-v2: Vivek pointed out that using cfq_get_cfqg() won't work if
     CONFIG_CFQ_GROUP_IOSCHED is disabled.  Fix it by factoring out
     initialization of base part of cfqg into cfq_init_cfqg_base() and
     alloc/init/free explicitly if !CONFIG_CFQ_GROUP_IOSCHED.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 3 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 7713c73d9590..5a1b8cc03003 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -540,9 +540,6 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
         if (err)
                 goto fail_id;
 
-        if (blk_throtl_init(q))
-                goto fail_id;
-
         setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
                     laptop_mode_timer_fn, (unsigned long) q);
         setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
@@ -565,6 +562,9 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
          */
         q->queue_lock = &q->__queue_lock;
 
+        if (blk_throtl_init(q))
+                goto fail_id;
+
         return q;
 
 fail_id: