linux-kernel - Re: cpumask: fix compat getaffinity

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Message-Id: <201005081111.08720.arnd@arndb.de>
Date:	Sat, 8 May 2010 11:11:08 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Andi Kleen <andi@...stfloor.org>,
	Ken Werner <ken.werner@....de>
Subject: Re: cpumask: fix compat getaffinity

On Saturday 08 May 2010 10:30:47 Rusty Russell wrote:
> 
> On Fri, 7 May 2010 10:15:49 pm Arnd Bergmann wrote:
> > Commit a45185d2d "cpumask: convert kernel/compat.c" broke
> > libnuma, which abuses sched_getaffinity to find out NR_CPUS
> > in order to parse /sys/devices/system/node/node*/cpumap.
> > 
> > On NUMA systems with less than 32 possibly CPUs, the
> > current compat_sys_sched_getaffinity now returns '4'
> > instead of the actual NR_CPUS/8, which makes libnuma
> > bail out when parsing the cpumap.
> 
> Really?  AFAICT the cpumap is printed using nr_cpu_ids too.  Can you
> give an example of what cpumap is on this system?

On Ken's PS3 running the Fedora 12 kernel (2.6.32-something), the output
from my memory is 00000000,00000000,00000000,00000003\n. NR_CPUs
is 128, nr_cpu_ids is most likely 2.

	Arnd
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