blkcg: update blkg_lookup_create() to do locking

To know when to create a blkg, the general pattern is to do a
blkg_lookup() and if that fails, lock and do the 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 <dennis@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 63d226a084cdefca691928585a30f60b7776735d..b421a9457e058be6c7a69af07cb8b37e7aab2969 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -249,7 +249,7 @@ err_free_blkg:
 }
 
 /**
- * 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
  *
@@ -262,8 +262,8 @@ err_free_blkg:
  * 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;
 
@@ -293,6 +293,28 @@ 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);
+
+       if (unlikely(!blkg)) {
+               spin_lock_irq(&q->queue_lock);
+               blkg = __blkg_lookup_create(blkcg, q);
+               spin_unlock_irq(&q->queue_lock);
+       }
+
+       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 fe0c4ca312ff621a988c1e81e5b193ba5c5ee5cb..e6f68f15dee98e8a7f939a15b8141bbe9d9d682e 100644 (file)
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -486,7 +486,7 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
        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);

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index f619307171a61381a678ff2884251bceb71f72a4..b3b1a8187d23271da15e3ac8ae22419a3e54e471 100644 (file)
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -181,6 +181,8 @@ 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);
@@ -799,7 +801,7 @@ 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);