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 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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index c19f907..cd0d97b 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -259,7 +259,7 @@ 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
  *
@@ -272,8 +272,8 @@ 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;
 
@@ -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 82450c3..ffde3ab 100644 (file)
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -407,7 +407,7 @@ 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 24067a1..cc0f238 100644 (file)
--- 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);