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Commit ec438699 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

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: default avatarTejun 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: default avatarJens Axboe <axboe@fb.com>
parent 496d5e75

block/bio.c

+1 −10
Original line number Diff line number Diff line
@@ -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;

}

include/linux/cgroup.h

+25 −0
Original line number Diff line number Diff line
@@ -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