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

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Message-Id: <200907291118.53912.rusty@rustcorp.com.au>
Date:	Wed, 29 Jul 2009 11:18:53 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Gregory Haskins <gregory.haskins@...il.com>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [regression] sched_getaffinity fails with EINVAL in 2.6.31-rc4

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.

I argued strongly against the set and getaffinity interfaces when they were
introduced; they can't be used in general without a loop (enlarge cpu_set,
retry).

Cheers,
Rusty.
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