cgroup: stash cgroup_root reference into cgroup_fs_context

Note that this reference is *NOT* contributing to refcount of
cgroup_root in question and is valid only until cgroup_do_mount()
returns.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 10 insertions, 4 deletions

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index a7b5a41f170c..3c1613a7648c 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -41,6 +41,7 @@ extern void __init enable_debug_cgroup(void);
  * The cgroup filesystem superblock creation/mount context.
  */
 struct cgroup_fs_context {
+        struct cgroup_root      *root;
         unsigned int    flags;                  /* CGRP_ROOT_* flags */
 
         /* cgroup1 bits */
@@ -208,7 +209,7 @@ int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
                           struct cgroup_namespace *ns);
 
 void cgroup_free_root(struct cgroup_root *root);
-void init_cgroup_root(struct cgroup_root *root, struct cgroup_fs_context *ctx);
+void init_cgroup_root(struct cgroup_fs_context *ctx);
 int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask);
 int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
 struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 725e9f6fe80d..45a198c63d6e 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -1208,6 +1208,7 @@ int cgroup1_get_tree(struct fs_context *fc)
                 if (root->flags ^ ctx->flags)
                         pr_warn("new mount options do not match the existing superblock, will be ignored\n");
 
+                ctx->root = root;
                 ret = 0;
                 goto out_unlock;
         }
@@ -1234,7 +1235,8 @@ int cgroup1_get_tree(struct fs_context *fc)
                 goto out_unlock;
         }
 
-        init_cgroup_root(root, ctx);
+        ctx->root = root;
+        init_cgroup_root(ctx);
 
         ret = cgroup_setup_root(root, ctx->subsys_mask);
         if (ret)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d0cddfbdf5cf..57f43f63363a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1915,8 +1915,9 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
         INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
 }
 
-void init_cgroup_root(struct cgroup_root *root, struct cgroup_fs_context *ctx)
+void init_cgroup_root(struct cgroup_fs_context *ctx)
 {
+        struct cgroup_root *root = ctx->root;
         struct cgroup *cgrp = &root->cgrp;
 
         INIT_LIST_HEAD(&root->root_list);
@@ -2098,6 +2099,7 @@ static int cgroup_get_tree(struct fs_context *fc)
 
         cgrp_dfl_visible = true;
         cgroup_get_live(&cgrp_dfl_root.cgrp);
+        ctx->root = &cgrp_dfl_root;
 
         root = cgroup_do_mount(&cgroup2_fs_type, fc->sb_flags, &cgrp_dfl_root,
                                          CGROUP2_SUPER_MAGIC, ns);
@@ -5374,7 +5376,8 @@ int __init cgroup_init_early(void)
         struct cgroup_subsys *ss;
         int i;
 
-        init_cgroup_root(&cgrp_dfl_root, &ctx);
+        ctx.root = &cgrp_dfl_root;
+        init_cgroup_root(&ctx);
         cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
 
         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);