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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>
This commit is contained in:
Tejun Heo 2015-05-22 17:13:22 -04:00 committed by Jens Axboe
parent 496d5e7560
commit ec438699a9
2 changed files with 26 additions and 10 deletions
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11
block/bio.c
View File

@ -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;
}

25
include/linux/cgroup.h
View File

@ -773,6 +773,31 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task,
return task_css_check(task, subsys_id, false);
}
/**
* 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