linux-kernel - [PATCH 4.18 016/145] blkcg: Introduce blkg_root

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Message-Id: <20180907210904.883199291@linuxfoundation.org>
Date:   Fri,  7 Sep 2018 23:08:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bart.vanassche@....com>,
        Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
        Ming Lei <ming.lei@...hat.com>, Omar Sandoval <osandov@...com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Alexandru Moise <00moses.alexander00@...il.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.18 016/145] blkcg: Introduce blkg_root_lookup()

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bart Van Assche <bart.vanassche@....com>

commit 6bad9b210a228d2fe0e0efe26d9b115348529cee upstream.

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 <bart.vanassche@....com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: Omar Sandoval <osandov@...com>
Cc: Johannes Thumshirn <jthumshirn@...e.de>
Cc: Alexandru Moise <00moses.alexander00@...il.com>
Cc: Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/blk-cgroup.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -296,6 +296,23 @@ static inline struct blkcg_gq *blkg_look
 }
 
 /**
+ * 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
  * @pol: policy of interest
@@ -737,6 +754,7 @@ struct blkcg_policy {
 #ifdef CONFIG_BLOCK
 
 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) { }