[PATCH 04/16] cgroup, block: implement task_get_css() and use it in bio_associate_current()
From: Tejun Heo <tj@kernel.org>
Date: 2015-01-06 19:29:05
Also in:
linux-fsdevel, linux-mm, lkml
Subsystem:
block layer, control group (cgroup), the rest · Maintainers:
Jens Axboe, Tejun Heo, Johannes Weiner, Michal Koutný, Linus Torvalds
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 <redacted> Cc: Jens Axboe <axboe@kernel.dk> Cc: Vivek Goyal <vgoyal@redhat.com> --- block/bio.c | 11 +---------- include/linux/cgroup.h | 25 +++++++++++++++++++++++++ 2 files changed, 26 insertions(+), 10 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 471d738..a1e0b00 100644
--- a/block/bio.c
+++ b/block/bio.c@@ -2031,7 +2031,6 @@ 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;
@@ -2040,17 +2039,9 @@ 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; }
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b9cb94c..e7da0aa 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h@@ -774,6 +774,31 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task, } /** + * task_get_css - find and get the css for (task, subsys) + * @task: the target task + * @subsys_id: the target subsystem ID + * + * Find the css for the (@task, @subsys_id) combination, increment a + * reference on and return it. This function is guaranteed to return a + * valid css. + */ +static inline struct cgroup_subsys_state * +task_get_css(struct task_struct *task, int subsys_id) +{ + struct cgroup_subsys_state *css; + + rcu_read_lock(); + while (true) { + css = task_css(task, subsys_id); + if (likely(css_tryget_online(css))) + break; + cpu_relax(); + } + rcu_read_unlock(); + return css; +} + +/** * task_css_is_root - test whether a task belongs to the root css * @task: the target task * @subsys_id: the target subsystem ID
--
2.1.0
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