cgroup: introduce cgroup_ino()

mm/memory-failure.c::hwpoison_filter_task() has been reaching into
cgroup to extract the associated ino to be used as a filtering
criterion.  This is an implementation detail which shouldn't be
depended upon from outside cgroup proper and is about to change with
the scheduled kernfs conversion.

This patch introduces a proper interface to determine the associated
ino, cgroup_ino(), and updates hwpoison_filter_task() to use it
instead of reaching directly into cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4f08a2d61487..9b5933c66c16 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -145,14 +145,10 @@ static int hwpoison_filter_task(struct page *p)
                 return -EINVAL;
 
         css = mem_cgroup_css(mem);
-        /* root_mem_cgroup has NULL dentries */
-        if (!css->cgroup->dentry)
-                return -EINVAL;
-
-        ino = css->cgroup->dentry->d_inode->i_ino;
+        ino = cgroup_ino(css->cgroup);
         css_put(css);
 
-        if (ino != hwpoison_filter_memcg)
+        if (!ino || ino != hwpoison_filter_memcg)
                 return -EINVAL;
 
         return 0;