cgroup: remove redundant variable in cgroup_mount()

Both pinned_sb and new_sb indicate if a new superblock is needed,
so we can just remove new_sb.

Note now we must check if kernfs_tryget_sb() returns NULL, because
when it returns NULL, kernfs_mount() may still re-use an existing
superblock, which is just allocated by another concurent mount.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f873c468131648fa422bdaab9adb2faf8230297c..5eb20cd1709c56956ace0820699bef5735475a77 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1694,7 +1694,6 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
        struct dentry *dentry;
        int ret;
        int i;
-       bool new_sb;
 
        /*
         * The first time anyone tries to mount a cgroup, enable the list
@@ -1785,7 +1784,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
                 * path is super cold.  Let's just sleep a bit and retry.
                 */
                pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
-               if (IS_ERR(pinned_sb) ||
+               if (IS_ERR_OR_NULL(pinned_sb) ||
                    !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
                        mutex_unlock(&cgroup_mutex);
                        if (!IS_ERR_OR_NULL(pinned_sb))
@@ -1831,18 +1830,16 @@ out_free:
                return ERR_PTR(ret);
 
        dentry = kernfs_mount(fs_type, flags, root->kf_root,
-                               CGROUP_SUPER_MAGIC, &new_sb);
-       if (IS_ERR(dentry) || !new_sb)
+                               CGROUP_SUPER_MAGIC, NULL);
+       if (IS_ERR(dentry) || pinned_sb)
                cgroup_put(&root->cgrp);
 
        /*
         * If @pinned_sb, we're reusing an existing root and holding an
         * extra ref on its sb.  Mount is complete.  Put the extra ref.
         */
-       if (pinned_sb) {
-               WARN_ON(new_sb);
+       if (pinned_sb)
                deactivate_super(pinned_sb);
-       }
 
        return dentry;
 }