cgroup1_get_tree(): separate "get cgroup_root to use" into a separate helper

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

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 05f05d7..0d71fc9 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -1135,7 +1135,15 @@ struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
        .show_path              = cgroup_show_path,
 };
 
-int cgroup1_get_tree(struct fs_context *fc)
+/*
+ * The guts of cgroup1 mount - find or create cgroup_root to use.
+ * Called with cgroup_mutex held; returns 0 on success, -E... on
+ * error and positive - in case when the candidate is busy dying.
+ * On success it stashes a reference to cgroup_root into given
+ * cgroup_fs_context; that reference is *NOT* counting towards the
+ * cgroup_root refcount.
+ */
+static int cgroup1_root_to_use(struct fs_context *fc)
 {
        struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
@@ -1143,16 +1151,10 @@ int cgroup1_get_tree(struct fs_context *fc)
        struct cgroup_subsys *ss;
        int i, ret;
 
-       /* Check if the caller has permission to mount. */
-       if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
-               return -EPERM;
-
-       cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
-
        /* First find the desired set of subsystems */
        ret = check_cgroupfs_options(fc);
        if (ret)
-               goto out_unlock;
+               return ret;
 
        /*
         * Destruction of cgroup root is asynchronous, so subsystems may
@@ -1166,12 +1168,8 @@ int cgroup1_get_tree(struct fs_context *fc)
                    ss->root == &cgrp_dfl_root)
                        continue;
 
-               if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
-                       mutex_unlock(&cgroup_mutex);
-                       msleep(10);
-                       ret = restart_syscall();
-                       goto out_free;
-               }
+               if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt))
+                       return 1;       /* restart */
                cgroup_put(&ss->root->cgrp);
        }
 
@@ -1200,16 +1198,14 @@ int cgroup1_get_tree(struct fs_context *fc)
                    (ctx->subsys_mask != root->subsys_mask)) {
                        if (!name_match)
                                continue;
-                       ret = -EBUSY;
-                       goto out_unlock;
+                       return -EBUSY;
                }
 
                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;
+               return 0;
        }
 
        /*
@@ -1217,22 +1213,16 @@ int cgroup1_get_tree(struct fs_context *fc)
         * specification is allowed for already existing hierarchies but we
         * can't create new one without subsys specification.
         */
-       if (!ctx->subsys_mask && !ctx->none) {
-               ret = cg_invalf(fc, "cgroup1: No subsys list or none specified");
-               goto out_unlock;
-       }
+       if (!ctx->subsys_mask && !ctx->none)
+               return cg_invalf(fc, "cgroup1: No subsys list or none specified");
 
        /* Hierarchies may only be created in the initial cgroup namespace. */
-       if (ns != &init_cgroup_ns) {
-               ret = -EPERM;
-               goto out_unlock;
-       }
+       if (ns != &init_cgroup_ns)
+               return -EPERM;
 
        root = kzalloc(sizeof(*root), GFP_KERNEL);
-       if (!root) {
-               ret = -ENOMEM;
-               goto out_unlock;
-       }
+       if (!root)
+               return -ENOMEM;
 
        ctx->root = root;
        init_cgroup_root(ctx);
@@ -1240,23 +1230,38 @@ int cgroup1_get_tree(struct fs_context *fc)
        ret = cgroup_setup_root(root, ctx->subsys_mask);
        if (ret)
                cgroup_free_root(root);
+       return ret;
+}
+
+int cgroup1_get_tree(struct fs_context *fc)
+{
+       struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
+       struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
+       int ret;
+
+       /* Check if the caller has permission to mount. */
+       if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+               return -EPERM;
+
+       cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
+
+       ret = cgroup1_root_to_use(fc);
+       if (!ret && !percpu_ref_tryget_live(&ctx->root->cgrp.self.refcnt))
+               ret = 1;        /* restart */
 
-out_unlock:
-       if (!ret && !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
-               mutex_unlock(&cgroup_mutex);
-               msleep(10);
-               return restart_syscall();
-       }
        mutex_unlock(&cgroup_mutex);
-out_free:
-       if (ret)
-               return ret;
 
-       ret = cgroup_do_mount(fc, CGROUP_SUPER_MAGIC, ns);
-       if (!ret && percpu_ref_is_dying(&root->cgrp.self.refcnt)) {
+       if (!ret)
+               ret = cgroup_do_mount(fc, CGROUP_SUPER_MAGIC, ns);
+
+       if (!ret && percpu_ref_is_dying(&ctx->root->cgrp.self.refcnt)) {
                struct super_block *sb = fc->root->d_sb;
                dput(fc->root);
                deactivate_locked_super(sb);
+               ret = 1;
+       }
+
+       if (unlikely(ret > 0)) {
                msleep(10);
                return restart_syscall();
        }