block: RCU free request_queue

RCU free request_queue so that blkcg_gq->q can be dereferenced under
RCU lock.  This will be used to implement hierarchical stats.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

block/blk-sysfs.c

@@ -497,6 +497,13 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr,
 	return res;
 }
 
+static void blk_free_queue_rcu(struct rcu_head *rcu_head)
+{
+	struct request_queue *q = container_of(rcu_head, struct request_queue,
+					       rcu_head);
+	kmem_cache_free(blk_requestq_cachep, q);
+}
+
 /**
  * blk_release_queue: - release a &struct request_queue when it is no longer needed
  * @kobj:    the kobj belonging to the request queue to be released
@@ -538,7 +545,7 @@ static void blk_release_queue(struct kobject *kobj)
 	bdi_destroy(&q->backing_dev_info);
 
 	ida_simple_remove(&blk_queue_ida, q->id);
-	kmem_cache_free(blk_requestq_cachep, q);
+	call_rcu(&q->rcu_head, blk_free_queue_rcu);
 }
 
 static const struct sysfs_ops queue_sysfs_ops = {

include/linux/blkdev.h

@@ -19,6 +19,7 @@
 #include <linux/gfp.h>
 #include <linux/bsg.h>
 #include <linux/smp.h>
+#include <linux/rcupdate.h>
 
 #include <asm/scatterlist.h>
 
@@ -437,6 +438,7 @@ struct request_queue {
 	/* Throttle data */
 	struct throtl_data *td;
 #endif
+	struct rcu_head		rcu_head;
 };
 
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */