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kernfs: do not account ino_ida allocations to memcg

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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 <vdavydov@parallels.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org>	[4.0.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vladimir Davydov 2015-05-14 15:16:58 -07:00 committed by Linus Torvalds
parent 8f4fc071b1
commit 499611ed45
1 changed files with 8 additions and 1 deletions
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9
fs/kernfs/dir.c
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@ -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;