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| author | Tejun Heo <tj@kernel.org> | 2015-05-22 17:13:22 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2015-06-02 08:33:34 -0600 |
| commit | ec438699a9ae0856c2ce20a50dd39cdc7e92a732 (patch) | |
| tree | f7406e5c235380474bf829639feed12bf0711101 | |
| parent | 496d5e7560dbb84399dbd92316fc33857aa83900 (diff) | |
| download | lwn-ec438699a9ae0856c2ce20a50dd39cdc7e92a732.tar.gz lwn-ec438699a9ae0856c2ce20a50dd39cdc7e92a732.zip | |
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>
| -rw-r--r-- | block/bio.c | 11 | ||||
| -rw-r--r-- | include/linux/cgroup.h | 25 |
2 files changed, 26 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; } diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index b9cb94c3102a..e7da0aa65b2d 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 |