[LTP] Question about kernel/syscall/signal/signal06.c

[Hongzhi, Song]

On 7/19/19 4:44 PM, Li Wang wrote:
> On Fri, Jul 19, 2019 at 4:14 PM Hongzhi, Song
> <hongzhi.song@windriver.com> wrote:
>> This case fails when boot qemux86-64 with 1/2 cores.
>>
>> I find [kernel 5.2-rc1: 0d714dba162] causes the failure by git bisect.

Hi Li,Wang


Sorry for my a bit mistake, the exact tag is [5.1-rc3 : 0d714dba162]

commit 0d714dba162620fd8b9f5b3104a487e041353c4d
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Wed Apr 3 18:41:48 2019 +0200

     x86/fpu: Update xstate's PKRU value on write_pkru()

     During the context switch the xstate is loaded which also includes the
     PKRU value.

     If xstate is restored on return to userland it is required
     that the PKRU value in xstate is the same as the one in the CPU.

     Save the PKRU in xstate during modification.


>>
>> If git checkout a commit before 0d714dba162, the case will pass on the
>> same qemu configuration.
> It sounds like a new regression on fpu. I will have a try on this test then.
>
> @Hongzhi, could you provide more info of your test machine? (e.g.
> lscpu, uname -r)
> and test result with 1vcpu, 2vcpus?


I tested "-smp 1/2/4" and "-cpu Skylake-Client-IBRS/core2duo", all of 
them failed.


1. This is my qemu boot cmdline:

qemu-system-x86_64 -device 
virtio-net-pci,netdev=net0,mac=52:54:00:12:35:02 -netdev 
user,id=net0,hostfwd=tcp::2222-:22,hostfwd=tcp::2323-:23,tftp=images/qemux86-64 
-drive file=image.rootfs.ext4,if=virtio,format=raw -vga vmware 
-show-cursor -usb -device usb-tablet -object 
rng-random,filename=/dev/urandom,id=rng0 -device 
virtio-rng-pci,rng=rng0  -nographic  -m 256  -cpu Skylake-Client-IBRS 
-serial mon:stdio -serial null -kernel linux/arch/x86/boot/bzImage 
-append 'root=/dev/vda rw highres=off console=ttyS0 mem=256M ip=dhcp 
vga=0 uvesafb.mode_option=640x480-32 oprofile.timer=1 
uvesafb.task_timeout=-1 '

2. lscpu

root@qemux86-64:~# lscpu
Architecture:                    x86_64
CPU op-mode(s):              32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                 40 bits physical, 48 bits virtual
CPU(s):                            4
On-line CPU(s) list:           0
Thread(s) per core:          1
Core(s) per socket:          1
Socket(s):                        1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                             94
Model name:                   Intel Core Processor (Skylake, IBRS)
Stepping:                        3
CPU MHz:                        3100.012
BogoMIPS:                       6200.02
L1d cache:                      32 KiB
L1i cache:                       32 KiB
L2 cache:                        4 MiB
L3 cache:                        16 MiB
Vulnerability L1tf:            Mitigation; PTE Inversion
Vulnerability Meltdown:   Mitigation; PTI
Vulnerability Spec store bypass: Vulnerable
Vulnerability Spectre v1:        Mitigation; __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, 
STIBP disab
                                  led, RSB filling
Flags:                           fpu de pse tsc msr pae mce cx8 apic sep 
mtrr pg
                                  e mca cmov pat pse36 clflush mmx fxsr 
sse sse2
                                  syscall nx rdtscp lm constant_tsc 
rep_good nopl
                                   xtopology cpuid pni pclmulqdq ssse3 
cx16 sse4_
                                  1 sse4_2 movbe popcnt aes xsave 
hypervisor lahf
                                  _lm abm pti fsgsbase bmi1 smep bmi2 
erms adx sm
                                  ap xsaveopt xgetbv1 arat


3.  uname -r

root@qemux86-64:~# uname -r
5.1.0-rc3-Linux-standard


Thanks.

--Hongzhi


>
> [Ccing fpu Dev in this loop]
>
>>
>> --Hongzhi
>>
>>
>> On 7/17/19 5:46 PM, Cyril Hrubis wrote:
>>> Hi!
>>>> I find signal06 fails on qemux86-64 when qemu has a small number cores,
>>>> e.g. "qemu -smp 1/2/4/6".
>>>>
>>>> ERROR INFO:
>>>>
>>>> signal06?????? 0?? TINFO?? :?? loop = 23
>>>> signal06?????? 1?? TFAIL?? :?? signal06.c:87: Bug Reproduced!
>>>>
>>>> But if boot qemu with "-smp 16", the case has great chance to pass.
>>>>
>>>>
>>>> I have two questions about this case:
>>>>
>>>> 1. I don't know why multi-core will affect the case.
>>> Have you looked into the code? The test is trying to reproduce a race
>>> condition between two threads of course the number of cores does affect
>>> the reproducibility.
>>>
>>>> 2. On failure situation, what does break the "while loop" shown in below
>>>> code.
>>> Bug in a kernel that fails to restore fpu state.
>>>
>
>