Re: [RFC] [PATCH] sched_getaffinity() fails with -EINVAL

[Sharyathi Nagesh <sharyath at in dot ibm dot com>]

Carlos/Bert
	Thanks for your advice.
Here I am submitting the patch as you have suggested, please let me know if I have to mail 
it to libc mailing list (libc-alpha) or raise a bugzilla request.

========================================================================
Explanation:
 	We are observing that ltp test case getcpu01.c is failing in some of the machines. In the 
test case: system call to sched_getaffinity() fails. Linux kernel is giving EINVAL on call 
to sched_getaffinity().
	
-----------------------------------------------------------------------
When I execute the test case:

#include<stdio.h>
#include<errno.h>
#define _GNU_SOURCE
#include<sched.h>

int main()
{
    cpu_set_t set;
    if (sched_getaffinity(0, sizeof(cpu_set_t), &set) < 0)
        printf("\n Call is failing with:%d", errno);
}


I get this error message
    "Call is failing with:22"
-----------------------------------------------------------------------
Further analysis revealed that this EINVAL error message is coming from this part of Linux 
kernel code.

SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        int ret;
        cpumask_var_t mask;

        if (len < cpumask_size())
                return -EINVAL;      <== This is where the error messages is coming from


cpumask_size() returns 512 when 'configure maximum number of SMP processors and NUMA node' 
option is enabled in kernel config. Since len is only 128 (sizeof(cpu_set_t)) system call 
fails with EINVAL.
    In the sense user end glibc allows only 1024 CPU bits in cpu_set_t when kernel can 
support 4096 cpus/bits. This patch is to increase the size of this data structure.

========================================================================
Testing:
    There was no regression observed when tested on x86-linux-gnu box with older kernel. 
Kernel in this case was 2.6.16 and application was built as 32 bit.
========================================================================
FSF copyright assignment
    My current FSF copy right assignment is in approved status.
========================================================================
GNU Changelog

2009-10-30  Sharyathi Nagesh  <sharyathi@in.ibm.com>

	* bits/sched.c (__CPU_SETSIZE): Size of the cpu_set_t data structure is changed to 
   	4096 bits from earlier 1024 bits to reflect changes in the Linux kernel.		

========================================================================

Thanks
Yeehaw

Index: glibc/bits/sched.h
===================================================================
--- glibc.orig/bits/sched.h	2009-10-29 11:09:30.000000000 +0530
+++ glibc/bits/sched.h	2009-10-29 12:14:20.000000000 +0530
@@ -38,7 +38,7 @@
 #if defined _SCHED_H && !defined __cpu_set_t_defined
 # define __cpu_set_t_defined
 /* Size definition for CPU sets.  */
-# define __CPU_SETSIZE	1024
+# define __CPU_SETSIZE	4096
 # define __NCPUBITS	(8 * sizeof (__cpu_mask))
 
 /* Type for array elements in 'cpu_set'.  */