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, 4 insertions, 1 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 42e588ef62d1..11f7a05e791e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -792,7 +792,10 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
         struct inode *inode = new_inode(sb);
 
         if (inode) {
-                inode->i_ino = get_next_ino();
+                do {
+                        /* ino 0 is reserved for dummy_root */
+                        inode->i_ino = get_next_ino();
+                } while (!inode->i_ino);
                 inode->i_mode = mode;
                 inode->i_uid = current_fsuid();
                 inode->i_gid = current_fsgid();