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Subject[PATCH 02/12] blkcg: update blkg_lookup_create to do locking
Date
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
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