cgroup: add cgroup_get_from_file() helper

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
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9ca51bf..16fe1c6 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5880,6 +5880,24 @@ 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.
@@ -6171,7 +6189,6 @@ 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;
 
@@ -6179,17 +6196,8 @@ 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);