Re: [Suggestion] kernel/cgroup.c: about kfree after 'get_new_cssid'

Chen Gang
2013-05-07T11:20:49Z

On 2013年05月07日 19:01, Li Zefan wrote:
> On 2013/5/7 18:46, Chen Gang wrote:
>> Hello Maintainers:
>>
>> After call get_new_cssid(), I can not find the related free function
>> (it seems free_css_id() is for that, but not used).
>>
>> The memory location is:
>> get_new_cssid() --> kzalloc() for 'struct css_id'
>> get_new_cssid() --> idr_alloc() for 'ss->idr'
>>
>> One work flow:
>> cgroup_load_subsys() --> cgroup_init_idr() --> get_new_cssid()
>> when get_new_cssid() fails, it will:
>> cgroup_load_subsys() --> cgroup_unload_subsys() --> idr_destroy(),
>> and also:
>> cgroup_load_subsys() --> cgroup_unload_subsys() --> ss->css_free();
>> ('css_free' may 'debug_css_free', or 'freezer_css_free' ...)
>>
>> It seems the work flow above is not 'kfree' 'struct css_id', is it true?
>>
>> BTW: I also guess, for cgroup_init_idr() in cgroup_init(), need check
>> the return value.
>>
>> Please help check.
>>
>
> It's the specific cgroup subsystem that calls free_css_id() in it's subsys->css_free()
> callback. See __mem_cgroup_free() for example.
>

OK, thank you for your confirmation.

> There's a bug in cgroup_unload_subsys() that idr_destroy() should be called after
> ss->css_free(). That said, given there's no modular cgroup subsystem using css_id,
> and the whole css_id thing will be eliminated in 3.11, why bother fixing it.
>

I just find it by reading code (I also want to learn about kernel).

I guess, for some stable versions, may focus on it, they are the
different branches from the latest version.

So, is it suitable to send related patch for the bug ?