Re: [LTP] Regarding shmat01 syscall test

[Jan Stancek <jstancek@redhat.com>]

----- 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.

Regards,
Jan

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