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>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 63feaed83bc62c3263c6554e07bd9c4e854ad14b..06f577764414bba629be18c698fc51a821acd09c 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -507,6 +507,15 @@ static inline const char *cgroup_name(const struct cgroup *cgrp)
        return rcu_dereference(cgrp->name)->name;
 }
 
+/* returns ino associated with a cgroup, 0 indicates unmounted root */
+static inline ino_t cgroup_ino(struct cgroup *cgrp)
+{
+       if (cgrp->dentry)
+               return cgrp->dentry->d_inode->i_ino;
+       else
+               return 0;
+}
+
 static inline struct cgroup_subsys_state *seq_css(struct seq_file *seq)
 {
        struct cgroup_open_file *of = seq->private;

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 42e588ef62d1ffb8d497952396cc8644065b8ca3..11f7a05e791ee413ec250841b7dea89947bcae79 100644 (file)
--- 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();

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4f08a2d61487f3c45dc01638c31b6aff689ce6e7..9b5933c66c165d9b5fea0164b639187d82157988 100644 (file)
--- 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;