blkcg: Introduce blkg_root_lookup()

KAGA-KOKO · axboe · commit 6bad9b210a22 · 2018-08-09T09:12:57.000-06:00
This new function will be used in a later patch to verify whether a
queue has been dissociated from the cgroup controller before being
released.

Signed-off-by: Bart Van Assche &lt;bart.vanassche@wdc.com&gt;
Cc: Tejun Heo &lt;tj@kernel.org&gt;
Cc: Christoph Hellwig &lt;hch@lst.de&gt;
Cc: Ming Lei &lt;ming.lei@redhat.com&gt;
Cc: Omar Sandoval &lt;osandov@fb.com&gt;
Cc: Johannes Thumshirn &lt;jthumshirn@suse.de&gt;
Cc: Alexandru Moise &lt;00moses.alexander00@gmail.com&gt;
Cc: Joseph Qi &lt;joseph.qi@linux.alibaba.com&gt;
Cc: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
@@ -341,6 +341,23 @@ static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
 	return __blkg_lookup(blkcg, q, false);
 }
 
+/**
+ * blkg_lookup - look up blkg for the specified request queue
+ * @q: request_queue of interest
+ *
+ * Lookup blkg for @q at the root level. See also blkg_lookup().
+ */
+static inline struct blkcg_gq *blkg_root_lookup(struct request_queue *q)
+{
+	struct blkcg_gq *blkg;
+
+	rcu_read_lock();
+	blkg = blkg_lookup(&blkcg_root, q);
+	rcu_read_unlock();
+
+	return blkg;
+}
+
 /**
  * blkg_to_pdata - get policy private data
  * @blkg: blkg of interest
@@ -864,6 +881,7 @@ static inline bool blk_cgroup_congested(void) { return false; }
 static inline void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay) { }
 
 static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
+static inline struct blkcg_gq *blkg_root_lookup(struct request_queue *q) { return NULL; }
 static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
 static inline void blkcg_drain_queue(struct request_queue *q) { }
 static inline void blkcg_exit_queue(struct request_queue *q) { }
