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authorTejun Heo <tj@kernel.org>2015-05-22 17:13:22 -0400
committerJens Axboe <axboe@fb.com>2015-06-02 08:33:34 -0600
commitec438699a9ae0856c2ce20a50dd39cdc7e92a732 (patch)
treef7406e5c235380474bf829639feed12bf0711101
parent496d5e7560dbb84399dbd92316fc33857aa83900 (diff)
downloadblackbird-op-linux-ec438699a9ae0856c2ce20a50dd39cdc7e92a732.tar.gz
blackbird-op-linux-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.c11
-rw-r--r--include/linux/cgroup.h25
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
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