The patch titled
Subject: memcg: fix bad behavior in use_hierarchy file
has been added to the -mm tree. Its filename is
memcg-fix-bad-behavior-in-use_hierarchy-file.patch
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From: Glauber Costa <glommer@xxxxxxxxxxxxx>
Subject: memcg: fix bad behavior in use_hierarchy file
I have an application that does the following:
* copy the state of all controllers attached to a hierarchy
* replicate it as a child of the current level.
I would expect writes to the files to mostly succeed, since they are
inheriting sane values from parents.
But that is not the case for use_hierarchy. If it is set to 0, we succeed
ok. If we're set to 1, the value of the file is automatically set to 1 in
the children, but if userspace tries to write the very same 1, it will
fail. That same situation happens if we set use_hierarchy, create a
child, and then try to write 1 again.
Now, there is no reason whatsoever for failing to write a value that is
already there. It doesn't even match the comments, that states:
/* If parent's use_hierarchy is set, we can't make any modifications
* in the child subtrees...
since we are not changing anything.
So test the new value against the one we're storing, and automatically
return 0 if we're not proposing a change.
Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Cc: Dhaval Giani <dhaval.giani@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN mm/memcontrol.c~fix-bad-behavior-in-use_hierarchy-file mm/memcontrol.c
--- a/mm/memcontrol.c~fix-bad-behavior-in-use_hierarchy-file
+++ a/mm/memcontrol.c
@@ -3764,6 +3764,10 @@ static int mem_cgroup_hierarchy_write(st
parent_memcg = mem_cgroup_from_cont(parent);
cgroup_lock();
+
+ if (memcg->use_hierarchy == val)
+ goto out;
+
/*
* If parent's use_hierarchy is set, we can't make any modifications
* in the child subtrees. If it is unset, then the change can
@@ -3780,6 +3784,8 @@ static int mem_cgroup_hierarchy_write(st
retval = -EBUSY;
} else
retval = -EINVAL;
+
+out:
cgroup_unlock();
return retval;
_
Subject: Subject: memcg: fix bad behavior in use_hierarchy file
Patches currently in -mm which might be from glommer@xxxxxxxxxxxxx are
linux-next.patch
slab-move-full-state-transition-to-an-initcall.patch
memcg-rename-config-variables.patch
memcg-fix-bad-behavior-in-use_hierarchy-file.patch
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