On 12/04/2014 03:19 AM, Andrew Morton wrote:
> On Wed, 3 Dec 2014 15:25:24 -0800 Andrew Morton <a...@linux-foundation.org>
> wrote:
>
>> On Wed, 03 Dec 2014 15:41:21 +0300 Andrey Ryabinin <a.ryabi...@samsung.com>
>> wrote:
>>
>>>
>>> Use the 'unsigned long' type for 'zero' variable to fix this.
>>> Changing type to 'unsigned long' shouldn't affect any other users
>>> of this variable.
>>>
>>> Reported-by: Dmitry Vyukov <dvyu...@google.com>
>>> Fixes: ed4d4902ebdd ("mm, hugetlb: remove hugetlb_zero and
>>> hugetlb_infinity")
>>> Signed-off-by: Andrey Ryabinin <a.ryabi...@samsung.com>
>>> ---
>>> kernel/sysctl.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>>> index 15f2511..45c45c9 100644
>>> --- a/kernel/sysctl.c
>>> +++ b/kernel/sysctl.c
>>> @@ -120,7 +120,7 @@ static int sixty = 60;
>>>
>>> static int __maybe_unused neg_one = -1;
>>>
>>> -static int zero;
>>> +static unsigned long zero;
>>> static int __maybe_unused one = 1;
>>> static int __maybe_unused two = 2;
>>> static int __maybe_unused four = 4;
>>
>> Yeah, this is ghastly.
>>
>> Look at
>>
>> {
>> .procname = "numa_balancing",
>> .data = NULL, /* filled in by handler */
>> .maxlen = sizeof(unsigned int),
>> .mode = 0644,
>> .proc_handler = sysctl_numa_balancing,
>> .extra1 = &zero,
>> .extra2 = &one,
>> },
>>
>> Now extra1 points at a long and extra2 points at an int.
>> sysctl_numa_balancing() calls proc_dointvec_minmax() and I think your
>> patch just broke big-endian 64-bit machines. "sched_autogroup_enabled"
>> breaks as well.
>
> Taking another look at this...
>
> numa_balancing will continue to work on big-endian because of course
> zero is still zero when byteswapped. But that's such a hack, isn't
> documented and doesn't work for "one", "sixty", etc.
>
Yeah, I agree it's a bit hacky.
> I'm thinking a better fix here is to switch hugetlb_sysctl_handler to
> use `int's. 2^32 hugepages is enough for anybody.
>
It's 8 petabytes for 2MB pages, so yeah should be enough.
Perhaps it also makes sense to change types for counters in 'struct hstate'
from longs to ints.
> hugetlb_overcommit_handler() will need conversion also.
>
> Perhaps auditing all the proc_doulongvec_minmax callsites is the way to
> attack this.
>
I've looked through this yesterday and didn't found anything obviously wrong.
Though I could easily miss something.
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