[PATCH v4 2/6] cgroup: add cgroup_get_from_file() helper

Christian Brauner
2020-01-17T18:12:36Z

Add a helper cgroup_get_from_file(). The helper will be used in
subsequent patches to retrieve a cgroup while holding a reference to the
struct file it was taken from.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: cgroups@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v1 */
patch not present

/* v2 */
patch not present

/* v3 */
Link: https://lore.kernel.org/r/20200117002143.15559-3-christian.brauner@ubuntu.com
patch introduced
- Tejun Heo <tj@kernel.org>:
- split cgroup_get_from_file() changes into separate commmit

/* v4 */
unchanged
---
kernel/cgroup/cgroup.c | 30 +++++++++++++++++++-----------
1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ad1f9fea5c14..f05efc2677c8 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5882,6 +5882,24 @@ void cgroup_fork(struct task_struct *child)
INIT_LIST_HEAD(&child->cg_list);
}

+static struct cgroup *cgroup_get_from_file(struct file *f)
+{
+ struct cgroup_subsys_state *css;
+ struct cgroup *cgrp;
+
+ css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
+ if (IS_ERR(css))
+ return ERR_CAST(css);
+
+ cgrp = css->cgroup;
+ if (!cgroup_on_dfl(cgrp)) {
+ cgroup_put(cgrp);
+ return ERR_PTR(-EBADF);
+ }
+
+ return cgrp;
+}
+
/**
* cgroup_can_fork - called on a new task before the process is exposed
* @child: the task in question.
@@ -6170,7 +6188,6 @@ EXPORT_SYMBOL_GPL(cgroup_get_from_path);
*/
struct cgroup *cgroup_get_from_fd(int fd)
{
- struct cgroup_subsys_state *css;
struct cgroup *cgrp;
struct file *f;

@@ -6178,17 +6195,8 @@ struct cgroup *cgroup_get_from_fd(int fd)
if (!f)
return ERR_PTR(-EBADF);

- css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
+ cgrp = cgroup_get_from_file(f);
fput(f);
- if (IS_ERR(css))
- return ERR_CAST(css);
-
- cgrp = css->cgroup;
- if (!cgroup_on_dfl(cgrp)) {
- cgroup_put(cgrp);
- return ERR_PTR(-EBADF);
- }
-
return cgrp;
}
EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
--
2.25.0