cgroup, block: implement task_get_css() and use it in bio_associate_current()

bio_associate_current() currently open codes task_css() and
css_tryget_online() to find and pin $current's blkcg css.  Abstract it
into task_get_css() which is implemented from cgroup side.  As a task
is always associated with an online css for every subsystem except
while the css_set update is propagating, task_get_css() retries till
css_tryget_online() succeeds.

This is a cleanup and shouldn't lead to noticeable behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 10 deletions

diff --git a/block/bio.c b/block/bio.c
index 259197d97de1..c4f87018fb79 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2004,7 +2004,6 @@ EXPORT_SYMBOL(bioset_create_nobvec);
 int bio_associate_current(struct bio *bio)
 {
         struct io_context *ioc;
-        struct cgroup_subsys_state *css;
 
         if (bio->bi_ioc)
                 return -EBUSY;
@@ -2013,17 +2012,9 @@ int bio_associate_current(struct bio *bio)
         if (!ioc)
                 return -ENOENT;
 
-        /* acquire active ref on @ioc and associate */
         get_io_context_active(ioc);
         bio->bi_ioc = ioc;
-
-        /* associate blkcg if exists */
-        rcu_read_lock();
-        css = task_css(current, blkio_cgrp_id);
-        if (css && css_tryget_online(css))
-                bio->bi_css = css;
-        rcu_read_unlock();
-
+        bio->bi_css = task_get_css(current, blkio_cgrp_id);
         return 0;
 }