Re: [regression] sched_getaffinity fails with EINVAL in 2.6.31-rc4

Gregory Haskins
2009-07-29T03:48:59Z

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Rusty Russell wrote:
> On Tue, 28 Jul 2009 03:42:15 am David Rientjes wrote:
>> On Mon, 27 Jul 2009, Gregory Haskins wrote:
>>
>>> I am not sure when this started, but noticed that sched_getaffinity is
>>> not working in -rc4.
>>>
>>> [pid 6254] sched_getaffinity(0, 128, 0x7f80586b1fe0) = -1 EINVAL
>>> (Invalid argument)
>>>
>>> Here is a simple program for reproduction:
>>>
>>> #include <sched.h>
>>>
>>> int main(void)
>>> {
>>> cpu_set_t mask;
>>> int ret;
>>>
>>> ret = sched_getaffinity(0, sizeof(mask), &mask);
>>> if (ret < 0)
>>> perror("getaffinity");
>>>
>>> return ret;
>>> }
>>>
>>> If I get time, I will bisect this later today.
>>>
>> It's most likely due to the cpumask changes. I don't know what cpu_set_t
>> is, but it's probably smaller than CONFIG_NR_CPUS rounded up to a multiple
>> of sizeof(long).
>
> It's simply that you finally ran this on a kernel which had
> CONFIG_NR_CPUS > 1024.

Indeed. I thought I had replied to the list that I figured that out,
but I think it might have been a trimmed list from someone elses reply.

Long story short, MAXSMP=y crept in, which set NR_CPUS=4096. Backing
this off < 1024 indeed fixes the issue.

Thanks to all who replied!
-Greg

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