kernfs: do not account ino_ida allocations to memcg

root->ino_ida is used for kernfs inode number allocations. Since IDA has
a layered structure, different IDs can reside on the same layer, which
is currently accounted to some memory cgroup. The problem is that each
kmem cache of a memory cgroup has its own directory on sysfs (under
/sys/fs/kernel/<cache-name>/cgroup). If the inode number of such a
directory or any file in it gets allocated from a layer accounted to the
cgroup which the cache is created for, the cgroup will get pinned for
good, because one has to free all kmem allocations accounted to a cgroup
in order to release it and destroy all its kmem caches. That said we
must not account layers of ino_ida to any memory cgroup.

Since per net init operations may create new sysfs entries directly
(e.g. lo device) or indirectly (nf_conntrack creates a new kmem cache
per each namespace, which, in turn, creates new sysfs entries), an easy
way to reproduce this issue is by creating network namespace(s) from
inside a kmem-active memory cgroup.

Signed-off-by: Vladimir Davydov <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: <[email protected]>	[4.0.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index f131fc23ffc4c18f03a9764973fa998bf0e5f79e..fffca9517321c88ee1e0128b864b257c56e2350d 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -518,7 +518,14 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
        if (!kn)
                goto err_out1;
 
-       ret = ida_simple_get(&root->ino_ida, 1, 0, GFP_KERNEL);
+       /*
+        * If the ino of the sysfs entry created for a kmem cache gets
+        * allocated from an ida layer, which is accounted to the memcg that
+        * owns the cache, the memcg will get pinned forever. So do not account
+        * ino ida allocations.
+        */
+       ret = ida_simple_get(&root->ino_ida, 1, 0,
+                            GFP_KERNEL | __GFP_NOACCOUNT);
        if (ret < 0)
                goto err_out2;
        kn->ino = ret;