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, 9 insertions, 9 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 6613de78e364..aeeb798d1cda 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1252,7 +1252,6 @@ void blk_throtl_drain(struct request_queue *q)
 int blk_throtl_init(struct request_queue *q)
 {
         struct throtl_data *td;
-        struct throtl_grp *tg;
 
         td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
         if (!td)
@@ -1265,19 +1264,20 @@ int blk_throtl_init(struct request_queue *q)
 
         /* alloc and Init root group. */
         td->queue = q;
-        tg = throtl_alloc_tg(td);
 
-        if (!tg) {
-                kfree(td);
-                return -ENOMEM;
-        }
+        rcu_read_lock();
+        spin_lock_irq(q->queue_lock);
 
-        td->root_tg = tg;
+        td->root_tg = throtl_get_tg(td, &blkio_root_cgroup);
 
-        rcu_read_lock();
-        throtl_init_add_tg_lists(td, tg, &blkio_root_cgroup);
+        spin_unlock_irq(q->queue_lock);
         rcu_read_unlock();
 
+        if (!td->root_tg) {
+                kfree(td);
+                return -ENOMEM;
+        }
+
         /* Attach throtl data to request queue */
         q->td = td;
         return 0;