Re: [LTP] Regarding shmat01 syscall test

Wanlong Gao
2012-10-26T08:03:15Z

On 10/26/2012 04:01 PM, Jan Stancek wrote:
>
>
> ----- Original Message -----
>> From: "Wanlong Gao" <gaowanlong@cn.fujitsu.com>
>> To: "Jan Stancek" <jstancek@redhat.com>
>> Cc: ltp-list@lists.sourceforge.net, "Om Prakash PAL" <omprakash.pal@stericsson.com>
>> Sent: Friday, 26 October, 2012 3:45:31 AM
>> Subject: Re: [LTP] Regarding shmat01 syscall test
>>
>> On 10/24/2012 04:20 PM, Jan Stancek wrote:
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Wanlong Gao" <gaowanlong@cn.fujitsu.com>
>>>> To: "Jan Stancek" <jstancek@redhat.com>
>>>> Cc: ltp-list@lists.sourceforge.net, "Om Prakash PAL"
>>>> <omprakash.pal@stericsson.com>
>>>> Sent: Wednesday, 24 October, 2012 9:51:59 AM
>>>> Subject: Re: [LTP] Regarding shmat01 syscall test
>>>>
>>>> On 10/24/2012 03:49 PM, Jan Stancek wrote:
>>>>>
>>>>>
>>>>> ----- Original Message -----
>>>>>> From: "Wanlong Gao" <gaowanlong@cn.fujitsu.com>
>>>>>> To: "Jan Stancek" <jstancek@redhat.com>
>>>>>> Cc: ltp-list@lists.sourceforge.net, "Om Prakash PAL"
>>>>>> <omprakash.pal@stericsson.com>
>>>>>> Sent: Wednesday, 24 October, 2012 9:03:16 AM
>>>>>> Subject: Re: [LTP] Regarding shmat01 syscall test
>>>>>>
>>>>>> On 10/24/2012 02:43 PM, Jan Stancek wrote:
>>>>>>>
>>>>>>>
>>>>>>> ----- Original Message -----
>>>>>>>> From: "Wanlong Gao" <gaowanlong@cn.fujitsu.com>
>>>>>>>> To: "Om Prakash PAL" <omprakash.pal@stericsson.com>
>>>>>>>> Cc: ltp-list@lists.sourceforge.net
>>>>>>>> Sent: Wednesday, 24 October, 2012 2:45:47 AM
>>>>>>>> Subject: Re: [LTP] Regarding shmat01 syscall test
>>>>>>>>
>>>>>>>> On 10/23/2012 06:05 PM, Om Prakash PAL wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> -----Original Message-----
>>>>>>>>> From: Wanlong Gao [mailto:gaowanlong@cn.fujitsu.com]
>>>>>>>>> Sent: Tuesday, October 23, 2012 3:07 PM
>>>>>>>>> To: Om Prakash PAL
>>>>>>>>> Cc: ltp-list@lists.sourceforge.net
>>>>>>>>> Subject: Re: [LTP] Regarding shmat01 syscall test
>>>>>>>>>
>>>>>>>>> On 10/23/2012 05:24 PM, Om Prakash PAL wrote:
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I am working on syscall test: shmat01.c
>>>>>>>>>>
>>>>>>>>>> I have some confusion:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> In setup() : it is allocating shared memory by shmget() and
>>>>>>>>>> then
>>>>>>>>>> attaching by shmat() and after that detaching the attached
>>>>>>>>>> address (i.e. shmdt())
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> if (shmdt((const void *)base_addr) == -1) {
>>>>>>>>>>
>>>>>>>>>> tst_brkm(TBROK, cleanup, "Couldn't detach
>>>>>>>>>> shared
>>>>>>>>>> memory");
>>>>>>>>>>
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> And again in main function it is using same "base_addr" as
>>>>>>>>>> attaching address,
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> addr = shmat(*(TC[i].shmid), base_addr+TC[i].offset,
>>>>>>>>>>
>>>>>>>>>> TC[i].flags);
>>>>>>>>>>
>>>>>>>>>> how can we ensure(100%) that base_addr (virtual) will be
>>>>>>>>>> free
>>>>>>>>>> till
>>>>>>>>>> this point for attaching?.
>>>>>>>>>
>>>>>>>>> Maybe we can't, but I didn't see any fail on this. Did you
>>>>>>>>> see
>>>>>>>>> any
>>>>>>>>> testing failure here?
>>>>>>>>>
>>>>>>>>> Yes, I got some failure and the reason of failure is : the
>>>>>>>>> address
>>>>>>>>> at which we want to attach is busy.
>>>>>>>>
>>>>>>>> OK, please feel free to send a patch, or can you tell us how
>>>>>>>> to
>>>>>>>> reproduce it?
>>>>>>>
>>>>>>> I recall I could reproduce it, if I added single printf:
>>>>>>> http://article.gmane.org/gmane.linux.ltp/16480
>>>>>>
>>>>>> Do you get a solution? Send out a patch?
>>>>>
>>>>> No, I haven't send any patch.
>>>>>
>>>>> About solution:
>>>>> I'm thinking, that instead of probing with shmat, we can mmap
>>>>> large
>>>>> chunk of memory,
>>>>> and then set base_addr somewhere in the middle and unmap the
>>>>> chunk.
>>>>> That is, using address that get_unmapped_area() is unlikely to
>>>>> pick.
>>>>
>>>> This idea seems good, bug how can you decide the size of this
>>>> "chunk
>>>> of memory"?
>>>
>>> Good question. How about starting with some large value, say 512M,
>>> and keep dividing by 2 until mmap succeeds?
>>
>> So, can you send out a patch to see if others have an objection?
>
> Sure, I'll have a look at this today.

That's nice. Thank you.

Regards,
Wanlong Gao

>
> Regards,
> Jan