Re: [RFC PATCH 1/1] mm/percpu.c: fix memory leakage issue when allocate a odd alignment area

From: zijun_hu
Date: Wed Oct 12 2016 - 04:45:29 EST

On 10/12/2016 04:25 PM, Michal Hocko wrote:
> On Wed 12-10-16 15:24:33, zijun_hu wrote:
>> On 10/12/2016 02:53 PM, Michal Hocko wrote:
>>> On Wed 12-10-16 08:28:17, zijun_hu wrote:
>>>> On 2016/10/12 1:22, Michal Hocko wrote:
>>>>> On Tue 11-10-16 21:24:50, zijun_hu wrote:
>>>>>> From: zijun_hu <zijun_hu@xxxxxxx>
>> should we have a generic discussion whether such patches which considers
>> many boundary or rare conditions are necessary.
> In general, I believe that kernel internal interfaces which have no
> userspace exposure shouldn't be cluttered with sanity checks.

you are right and i agree with you. but there are many internal interfaces
perform sanity checks in current linux sources

>> i found the following code segments in mm/vmalloc.c
>> static struct vmap_area *alloc_vmap_area(unsigned long size,
>> unsigned long align,
>> unsigned long vstart, unsigned long vend,
>> int node, gfp_t gfp_mask)
>> {
>> ...
>> BUG_ON(!size);
>> BUG_ON(offset_in_page(size));
>> BUG_ON(!is_power_of_2(align));
> See a recent Linus rant about BUG_ONs. These BUG_ONs are quite old and
> from a quick look they are even unnecessary. So rather than adding more
> of those, I think removing those that are not needed is much more
> preferred.
i notice that, and the above code segments is used to illustrate that
input parameter checking is necessary sometimes

>> should we make below declarations as conventions
>> 1) when we say 'alignment', it means align to a power of 2 value
>> for example, aligning value @v to @b implicit @v is power of 2
>> , align 10 to 4 is 12
> alignment other than power-of-two makes only very limited sense to me.
you are right and i agree with you.
>> 2) when we say 'round value @v up/down to boundary @b', it means the
>> result is a times of @b, it don't requires @b is a power of 2

i will write to linus to ask for opinions whether we should declare
the meaning of 'align' and 'round up/down' formally and whether such
patches are necessary