Re: [PATCH] memcg: Free spare array to avoid memory leak

[Sha Zhengju <handai.szj-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 03/09/2012 11:40 AM, KAMEZAWA Hiroyuki wrote:
> On Tue,  6 Mar 2012 20:13:24 +0800
> Sha Zhengju<handai.szj-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>  wrote:
>
>> From: Sha Zhengju<handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
>>
>> When the last event is unregistered, there is no need to keep the spare
>> array anymore. So free it to avoid memory leak.
>>
>> Signed-off-by: Sha Zhengju<handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
>>
>> ---
>>   mm/memcontrol.c |    6 ++++++
>>   1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 22d94f5..3c09a84 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -4412,6 +4412,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
>>   swap_buffers:
>>   	/* Swap primary and spare array */
>>   	thresholds->spare = thresholds->primary;
>> +	/* If all events are unregistered, free the spare array */
>> +	if (!new) {
>> +		kfree(thresholds->spare);
>> +		thresholds->spare = NULL;
>> +	}
>> +
> Could you clear thresholds->primary ? I don't like a pointer points to freed memory.
Do you meaning I should set ‘thresholds->primary = NULL‘ ？
But the following rcu_assign_pointer will do this :

+	/* If all events are unregistered, free the spare array */
+	if (!new) {
+		kfree(thresholds->spare);
+		thresholds->spare = NULL;
+	}
+
  	rcu_assign_pointer(thresholds->primary, new);<---------*HERE*

  	/* To be sure that nobody uses thresholds */