Re: [LTP] Regarding shmat01 syscall test

Jan Stancek
2012-10-24T07:49:42Z

----- 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.

Regards,
Jan

>
>
> Thanks,
> Wanlong Gao
>
> >
> > Regards,
> > Jan
> >