On Tue, Apr 16, 2013 at 4:58 AM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 12 Apr 2013 17:11:08 +0900 Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
>
>> > --- a/include/linux/res_counter.h
>> > +++ b/include/linux/res_counter.h
>> > @@ -54,7 +54,7 @@ struct res_counter {
>> > struct res_counter *parent;
>> > };
>> >
>> > -#define RESOURCE_MAX (unsigned long long)LLONG_MAX
>> > +#define RESOURCE_MAX (unsigned long long)ULLONG_MAX
>> >
>>
>> I don't think it's a good idea to change a user-visible value.
>
> The old value was a mistake, surely.
>
> RESOURCE_MAX shouldn't be in this header file - that is far too general
> a name. I suggest the definition be moved to res_counter.c. And the
> (unsigned long long) cast is surely unneeded if we're to use
> ULLONG_MAX.
>
>> > /**
>> > * Helpers to interact with userspace
>> > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
>> > index ff55247..6c35310 100644
>> > --- a/kernel/res_counter.c
>> > +++ b/kernel/res_counter.c
>> > @@ -195,6 +195,12 @@ int res_counter_memparse_write_strategy(const char *buf,
>> > if (*end != '\0')
>> > return -EINVAL;
>> >
>> > - *res = PAGE_ALIGN(*res);
>> > + /* Since PAGE_ALIGN is aligning up(the next page boundary),
>> > + * check the left space to avoid overflow to 0. */
>> > + if (RESOURCE_MAX - *res < PAGE_SIZE - 1)
>> > + *res = RESOURCE_MAX;
>> > + else
>> > + *res = PAGE_ALIGN(*res);
>> > +
>>
>> Current interface seems strange because we can set a bigger value than
>> the value which means "unlimited".
>
> I'm not sure what you mean by this?
>
>> So, how about some thing like:
>>
>> if (*res > RESOURCE_MAX)
>> return -EINVAL;
>> if (*res > PAGE_ALIGN(RESOURCE_MAX) - PAGE_SIZE)
>> *res = RESOURCE_MAX;
>> else
>> *res = PAGE_ALIGN(*res);
>>
>
> The first thing I'd do to res_counter_memparse_write_strategy() is to
> rename its second arg to `resp' then add a local called `res'. Because
> that function dereferences res far too often.
>
> Then,
>
> - *res = PAGE_ALIGN(*res);
> if (PAGE_ALIGN(res) >= res)
> res = PAGE_ALIGN(res);
> else
> res = RESOURCE_MAX; /* PAGE_ALIGN wrapped to zero */
>
> *resp = res;
> return 0;
>
Okay, this one is better.
Thanks,
Sha
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