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SubjectRe: [PATCH -last version] freezer_cg: disable writing freezer.state of root cgroup
Hello Li ! 

Li Zefan wrote:
> Li Zefan wrote:
>>> Acked-by: Paul Menage <menage@google.com>
>>>
>>> I might use the term "non-freezable" rather than "unfreezable".
>>>
>> My bad English :(
>>
>> patch updated. (some annoying leading tabs are also removed in the doc)
>>
>
> And I forgot to s/EIO/EINVAL in the document..
>
> This patch should be the last version.. Sorry for the bothering.
>
>
> ======================
>
> From: Li Zefan <lizf@cn.fujitsu.com>
> Date: Tue, 4 Nov 2008 15:26:29 +0800
> Subject: [PATCH] freezer_cg: disable writing freezer.state of root cgroup
>
> With this change, control file 'freezer.state' doesn't exist in root
> cgroup, making root cgroup unfreezable.
>
> I think it's reasonable to disallow freeze tasks in the root cgroup.
> And then we can avoid fork overhead when freezer subsystem is
> compiled but not used.
>
> Also make writing invalid value to freezer.state returns EINVAL
> rather than EIO. This is more consistent with other cgroup subsystem.
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> Acked-by: Paul Menage <menage@google.com>

It looks fine

Acked-by: Cedric Le Goater <clg@fr.ibm.com>

I've also tested it.

here's a minor comment,

I would make a small macro is_root_freezer() to show explicitly
what we are testing and use the CSS_ROOT bit to test. That's what
the CSS_ROOT bit is for Paul ?

if yes, here's a possible result is below.

C.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
---
kernel/cgroup_freezer.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
Index: 2.6.27-lxc/kernel/cgroup_freezer.c
===================================================================
--- 2.6.27-lxc.orig/kernel/cgroup_freezer.c
+++ 2.6.27-lxc/kernel/cgroup_freezer.c
@@ -47,6 +47,11 @@ static inline struct freezer *task_freez
struct freezer, css);
}

+static inline int is_root_freezer(struct freezer *freezer)
+{
+ return test_bit(CSS_ROOT, &freezer->css.flags);
+}
+
int cgroup_frozen(struct task_struct *task)
{
struct freezer *freezer;
@@ -190,6 +195,13 @@ static void freezer_fork(struct cgroup_s
freezer = task_freezer(task);
task_unlock(task);

+ /*
+ * The root cgroup is non-freezable, so we can skip the
+ * following check.
+ */
+ if (is_root_freezer(freezer))
+ return;
+
BUG_ON(freezer->state == CGROUP_FROZEN);
spin_lock_irq(&freezer->lock);
/* Locking avoids race with FREEZING -> THAWED transitions. */
@@ -363,6 +375,9 @@ static struct cftype files[] = {

static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
{
+ if (is_root_freezer(cgroup_freezer(cgroup)))
+ return 0;
+
return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
}

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