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>

1 files changed, 4 insertions, 7 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f873c4681316..5eb20cd1709c 100644
--- 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;
 }