![Wed Apr 09 08:00:23 2014 (8.7k) by Marcin.Wielgosz [...] imc.ch](/Ticket/Attachment/1348433/715563/A8621E59-23EC-4528-905B-AB181A79DD22%5B3%5D.png){kind=link}
| Subject: | Segfaults on some fc13 |
| Date: | Wed, 9 Apr 2014 11:57:34 +0000 |
| To: | "bug-Sys-CpuAffinity [...] rt.cpan.org" <bug-Sys-CpuAffinity [...] rt.cpan.org> |
| From: | Marcin Wielgosz <Marcin.Wielgosz [...] imc.ch> |
Hi,
I’ve been using highly modified version of your module and I found out that it tends to segfault on some of FC13 boxes(Linux and distribution is irrelevant here).
Program received signal SIGSEGV, Segmentation fault.
0x00000035e1682d84 in memset () from /lib64/libc.so.6
(gdb) backtrace
#0 0x00000035e1682d84 in memset () from /lib64/libc.so.6
#1 0x00000035e16c7dc4 in sched_getaffinity@@GLIBC_2.3.4 () from /lib64/libc.so.6
Here is a part of linux-sched_getaffinity.xs:
if(debug_flag) fprintf(stderr,"getaffinity0\n");
_set1 = &_set2;
if(debug_flag) fprintf(stderr,"getaffinity1 pid=%d size=%d cpuset=0x%d\n",
(int) pid, (int) CPU_SETSIZE, (int) _set1);
z = sched_getaffinity((pid_t) pid, CPU_SETSIZE, _set1);
if(debug_flag) fprintf(stderr,"getaffinity2\n”);
And some facts from /usr/include/bits/sched.h:
# define __CPU_SETSIZE 1024
typedef unsigned long int __cpu_mask; // size 4B
# define __NCPUBITS (8 * sizeof (__cpu_mask)) // 32
typedef struct
{
__cpu_mask __bits[__CPU_SETSIZE / __NCPUBITS]; // size 4B * [1024/32] = 128B
} cpu_set_t;
So, 'sched_getaffinity((pid_t) pid, CPU_SETSIZE, _set1)’ requests libc to fill out _set1(128B) and zero the rest up to 1024nth byte which is beyond the size of the structure and leads to segfaults. I’d recommend to replace CPU_SETSIZE with sizeof(_set2);
Secondly, this module works up to 32 cores and needs to be rewritten.
Marcin Wielgosz
System Integration Engineer
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