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From: Dennis Zhou <dennisszhou@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Josef Bacik <josef@toxicpanda.com>
Cc: kernel-team@fb.com, linux-block@vger.kernel.org,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
Subject: [PATCH 02/12] blkcg: update blkg_lookup_create to do locking
Date: Tue, 11 Sep 2018 14:41:27 -0400
Message-ID: <20180911184137.35897-3-dennisszhou@gmail.com> (raw)
In-Reply-To: <20180911184137.35897-1-dennisszhou@gmail.com>

From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>

To know when to create a blkg, the general pattern is to do a
blkg_lookup and if that fails, lock and then do a lookup again and if
that fails finally create. It doesn't make much sense for everyone who
wants to do creation to write this themselves.

This changes blkg_lookup_create to do locking and implement this
pattern. The old blkg_lookup_create is renamed to __blkg_lookup_create.
If a call site wants to do its own error handling or already owns the
queue lock, they can use __blkg_lookup_create. This will be used in
upcoming patches.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
---
 block/blk-cgroup.c         | 31 ++++++++++++++++++++++++++++---
 block/blk-iolatency.c      |  2 +-
 include/linux/blk-cgroup.h |  4 +++-
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c19f9078da1e..cd0d97bed83d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -259,7 +259,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 }
 
 /**
- * blkg_lookup_create - lookup blkg, try to create one if not there
+ * __blkg_lookup_create - lookup blkg, try to create one if not there
  * @blkcg: blkcg of interest
  * @q: request_queue of interest
  *
@@ -272,8 +272,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
  * value on error.  If @q is dead, returns ERR_PTR(-EINVAL).  If @q is not
  * dead and bypassing, returns ERR_PTR(-EBUSY).
  */
-struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
-				    struct request_queue *q)
+struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
+				      struct request_queue *q)
 {
 	struct blkcg_gq *blkg;
 
@@ -310,6 +310,31 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 	}
 }
 
+/**
+ * blkg_lookup_create - find or create a blkg
+ * @blkcg: target block cgroup
+ * @q: target request_queue
+ *
+ * This looks up or creates the blkg representing the unique pair
+ * of the blkcg and the request_queue.
+ */
+struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
+				    struct request_queue *q)
+{
+	struct blkcg_gq *blkg = blkg_lookup(blkcg, q);
+	unsigned long flags;
+
+	if (unlikely(!blkg)) {
+		spin_lock_irqsave(q->queue_lock, flags);
+
+		blkg = __blkg_lookup_create(blkcg, q);
+
+		spin_unlock_irqrestore(q->queue_lock, flags);
+	}
+
+	return blkg;
+}
+
 static void blkg_destroy(struct blkcg_gq *blkg)
 {
 	struct blkcg *blkcg = blkg->blkcg;
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 62fdd9002c29..22b2ff0440cc 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -410,7 +410,7 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio,
 	if (unlikely(!blkg)) {
 		if (!lock)
 			spin_lock_irq(q->queue_lock);
-		blkg = blkg_lookup_create(blkcg, q);
+		blkg = __blkg_lookup_create(blkcg, q);
 		if (IS_ERR(blkg))
 			blkg = NULL;
 		if (!lock)
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 24067a1f8b36..cc0f238530f6 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -184,6 +184,8 @@ extern struct cgroup_subsys_state * const blkcg_root_css;
 
 struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
 				      struct request_queue *q, bool update_hint);
+struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
+				      struct request_queue *q);
 struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
 				    struct request_queue *q);
 int blkcg_init_queue(struct request_queue *q);
@@ -897,7 +899,7 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 	blkg = blkg_lookup(blkcg, q);
 	if (unlikely(!blkg)) {
 		spin_lock_irq(q->queue_lock);
-		blkg = blkg_lookup_create(blkcg, q);
+		blkg = __blkg_lookup_create(blkcg, q);
 		if (IS_ERR(blkg))
 			blkg = NULL;
 		spin_unlock_irq(q->queue_lock);
-- 
2.17.1


  parent reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-11 18:41 [PATCH v3 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-11 18:41 ` [PATCH 01/12] blkcg: fix ref count issue with bio_blkcg using task_css Dennis Zhou
2018-09-11 18:41 ` Dennis Zhou [this message]
2018-09-11 18:41 ` [PATCH 03/12] blkcg: convert blkg_lookup_create to find closest blkg Dennis Zhou
2018-09-11 23:50   ` Tejun Heo
2018-09-11 18:41 ` [PATCH 04/12] blkcg: always associate a bio with a blkg Dennis Zhou
2018-09-11 18:41 ` [PATCH 05/12] blkcg: consolidate bio_issue_init to be a part of core Dennis Zhou
2018-09-11 18:41 ` [PATCH 06/12] blkcg: associate a blkg for pages being evicted by swap Dennis Zhou
2018-09-11 18:41 ` [PATCH 07/12] blkcg: associate writeback bios with a blkg Dennis Zhou
2018-09-11 18:41 ` [PATCH 08/12] blkcg: remove bio->bi_css and instead use bio->bi_blkg Dennis Zhou
2018-09-11 18:41 ` [PATCH 09/12] blkcg: remove additional reference to the css Dennis Zhou
2018-09-11 23:51   ` Tejun Heo
2018-09-11 18:41 ` [PATCH 10/12] blkcg: cleanup and make blk_get_rl use blkg_lookup_create Dennis Zhou
2018-09-11 18:41 ` [PATCH 11/12] blkcg: change blkg reference counting to use percpu_ref Dennis Zhou
2018-09-11 18:41 ` [PATCH 12/12] blkcg: rename blkg_try_get to blkg_tryget Dennis Zhou
2018-09-21 20:56 ` [PATCH v3 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-22  2:29   ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2018-09-06 21:10 [PATCH " Dennis Zhou
2018-09-06 21:10 ` [PATCH 02/12] blkcg: update blkg_lookup_create to do locking Dennis Zhou
2018-09-07  6:17   ` Liu Bo

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