Commit 499611ed authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds

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: default avatarVladimir Davydov <>
Acked-by: default avatarTejun Heo <>
Cc: Johannes Weiner <>
Cc: Michal Hocko <>
Cc: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Cc: Greg Thelen <>
Cc: Greg Kroah-Hartman <>
Cc: <>	[4.0.x]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 8f4fc071
......@@ -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,
if (ret < 0)
goto err_out2;
kn->ino = ret;
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