On 07/25/2014 11:32 AM, Xiaoguang Wang wrote:
> Hi,
>
> On 07/25/2014 02:39 PM, Stanislav Kholmanskikh wrote:
>>
>>
>> On 07/25/2014 09:38 AM, Xiaoguang Wang wrote:
>>> Hi,
>>>
>>> When we run sched_setaffinity01 in RHEL5.10GA, it occurs a segmentation
>>> fault.
>>> Below is the possible reason.
>>
>> Hi!
>>
>> I though I'd checked this test case on OL5 before submission. Let me check
>> it again.
>
> OL5 is based RHEL5?
Yes.
> If it is, please also check your CONFIG_NR_CPUS in kernel config file. If
> it's 1024 or greater,
> this case will not fail. In my environment, this value is 255, thanks!
I initially tested it with 2.6.39-400.212.1.el5uek on OL5, and it passed.
[root@ol5-x64 sched_setaffinity]# grep CONFIG_NR_CPUS
/boot/config-2.6.39-400.212.1.el5uek.debug
CONFIG_NR_CPUS=4096
Now I checked it with 2.6.18-371.3.1.0.1.el5 and it failed as you said:
[root@ol5-x64 sched_setaffinity]# grep CONFIG_NR_CPUS
/boot/config-2.6.18-371.3.1.0.1.el5
CONFIG_NR_CPUS=255
Thanks for your findings.
I would also vote for the ltp_syscall(__NR_sched_setaffinity, ...)
variant proposed by Jan.
>
> Regards,
> Xiaoguang Wang
>>
>>>
>>> Hi Jan, would you please help to confirm this problem. I'm afraid
>>> RHEL5.10GA is an old
>>> distribution, which many people may not use it now, thanks!
>>>
>>>
>>> Glibc provides a encapsulation for the raw kernel sched_setaffinity(2)
>>> system call,
>>> the corresponding code is below(The version of glibc I used is
>>> glibc-2.5-20061008T1257-RHEL5.11Beta):
>>> I delete some code just for simple.
>>>
>>> #######################################################################################
>>>
>>> /* Size definition for CPU sets. */
>>> # define __CPU_SETSIZE 1024
>>> # define __NCPUBITS (8 * sizeof (__cpu_mask))
>>>
>>> /* Type for array elements in 'cpu_set'. */
>>> typedef unsigned long int __cpu_mask;
>>>
>>> /* Basic access functions. */
>>> # define __CPUELT(cpu) ((cpu) / __NCPUBITS)
>>>
>>> /* Data structure to describe CPU mask. */
>>> typedef struct
>>> {
>>> __cpu_mask __bits[__CPU_SETSIZE / __NCPUBITS];
>>> } cpu_set_t;
>>>
>>>
>>> int __sched_setaffinity_new (pid_t pid, size_t cpusetsize, const cpu_set_t
>>> *cpuset)
>>> {
>>> if (__builtin_expect (__kernel_cpumask_size == 0, 0))
>>> {
>>> int res;
>>>
>>> while (res = INTERNAL_SYSCALL (sched_getaffinity, err, 3, getpid (),
>>> psize, p),
>>> INTERNAL_SYSCALL_ERROR_P (res, err)
>>> && INTERNAL_SYSCALL_ERRNO (res, err) == EINVAL)
>>> ....
>>>
>>> __kernel_cpumask_size = res;
>>> }
>>>
>>> /* We now know the size of the kernel cpumask_t. Make sure the user
>>> does not request to set a bit beyond that. */
>>> for (size_t cnt = __kernel_cpumask_size; cnt < cpusetsize; ++cnt)
>>> if (((char *) cpuset)[cnt] != '\0')
>>> {
>>> /* Found a nonzero byte. This means the user request cannot be
>>> fulfilled. */
>>> __set_errno (EINVAL);
>>> return -1;
>>> }
>>>
>>> return INLINE_SYSCALL (sched_setaffinity, 3, pid, cpusetsize, cpuset);
>>> }
>>> #######################################################################################
>>>
>>> Glibc in RHEL5.10GA does not provide CPU_ALLOC_SIZE marco, so in ltp
>>> testcases/kernel/syscalls/sched_setaffinity/sched_setaffinity.h,
>>> we define one.
>>> #######################################################################################
>>> #ifndef CPU_ALLOC_SIZE
>>> #define CPU_ALLOC_SIZE(size) sizeof(cpu_set_t)
>>> #endif
>>> #######################################################################################
>>>
>>> Then CPU_ALLOC_SIZE would always return 128 in RHEL5.10GA, that is when we
>>> test EFAULT for sched_setaffinity(2),
>>> the passed cpusetsize is 128. But look at __sched_setaffinity_new() above,
>>> it first call
>>> raw sched_getaffinity(2) to get the size of the kernel cpumask_t, In
>>> RHEL5.10GA,
>>> this value depends on CONFIG_NR_CPUS, if CONFIG_NR_CPUS is 255, the raw
>>> sched_getaffinity(2) will return 32.
>>> In this case, __kernel_cpumask_size would be 32, cpusetsize is 128. Give
>>> that we're testing
>>> EFAULT, cpuset is a invalid pointer, if cnt > 32, it will generate
>>> segmentation fault in glibc code,
>>> so this case exits abnormally
>>>
>>> As why this test case can run normally in RHEL6.5GA or RHEL7.0GA, it's
>>> because
>>> sched_getaffinity(2) in old kernel(RHEL5.10GA) return sizeof(cpumask_t),
>>> which totally depends on CONFIG_NR_CPUS.
>>> In newer kernel, sched_getaffinity(2) returns the smaller one between
>>> min_t(size_t, len, cpumask_size()),
>>> here len is the value passed to sched_getaffinity as cpusetsize,
>>> cpumask_size() is the max allowed length.
>>> so we can ensure __kernel_cpumask_size will never smaller cpusetsize, so
>>> the segmentation fault won't occur.
>>>
>>> So I also think CPU_ALLOC and CPU_ALLOC_SIZE is wrong in
>>> testcases/kernel/syscalls/sched_setaffinity/sched_setaffinity.h. We should
>>> refer to the implementation in glibc. or we define CPU_ALLOC_SIZE using raw
>>> sched_getaffinity as a workaround in older kernel . See below code:
>>> #########################################################################################
>>>
>>> int ret;
>>> cpu_set_t cst;
>>>
>>> memset(&cst, 0, sizeof(cst));
>>>
>>> ret = syscall(__NR_sched_getaffinity, getpid(),
>>> sizeof(cpu_set_t), &cst);
>>> if (ret < 0) {
>>> fprintf(stderr, "sched_getaffinity failed: %s\n",
>>> strerror(errno));
>>> return 1;
>>> } else {
>>> printf("length of bit mask the kernel uses to represent
>>> the CPU"
>>> ": %d\n", ret);
>>> }
>>> #########################################################################################
>>>
>>> Regards,
>>> Xiaoguang Wang
>>>
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>> .
>>
>
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