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>

1 files changed, 3 insertions, 1 deletions

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);