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Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-10-19 16:24:31


The title is a bit long. :-)

On Oct 19, 2012, at 3:30 PM, Gutierrez, Samuel K wrote:

> Hi Chris,
>
> Thanks for all the info. Below is what can go into the FAQ. Any suggestions?
>
> I'm trying to use the Cross Memory Attach (CMA) capability within the
> shared-memory (sm) BTL, but am getting: "mca_btl_sm_get_sync: process_vm_readv
> failed: 1." Why am I seeing this error message?
>
> This may be due to insufficient permissions. CMA's usage requirements are
> exactly the same as those required to successfully perform a ptrace wtih PTRACE_ATTACH.
>
> On some systems, a modification to /etc/sysctl.d/10-ptrace.conf is required.
>
> Change:
> kernel.yama.ptrace_scope = 1
>
> to
>
> kernel.yama.ptrace_scope = 0
>
> and restart your system so the change can take effect.
>
> Thanks,
>
> Sam
> ________________________________________
> From: devel-bounces_at_[hidden] [devel-bounces_at_[hidden]] on behalf of Christopher Yeoh [cyeoh_at_[hidden]]
> Sent: Thursday, October 18, 2012 5:57 PM
> To: devel_at_[hidden]
> Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
>
> Hi Sam,
>
> On Thu, 18 Oct 2012 15:08:59 +0000
> "Gutierrez, Samuel K" <samuel_at_[hidden]> wrote:
>>
>> I really appreciate your pointing me in the right direction. It turns
>> out that on this particular system had /etc/sysctl.d/10-ptrace.conf
>> was set to 1. Changing this to 0 fixed the problem. I'm not sure if
>> this is the best way of getting things to work, but is sufficient for
>> my purposes.
>
> Yes I think this is the best way to do it. The kernel side
> implementation of CMA does the same permission checking as as ptrace
> (checks to see if PTRACE_MODE_ATTACH would be permitted). A value of 1
> in that config file only allows you to ptrace direct child processes,
> whereas a 0 removes that restriction.
>
> You still need to either have CAP_SYS_PTRACE (eg am probably root) or
> have the same UID/GID as the target. So from a security point of view
> the only extra risk you have exposed your system to are bugs that may
> exist in the ptrace or CMA implementations.
>
> Regards,
>
> Chris
>
>> Thanks!
>>
>> Sam
>> ________________________________
>> From: devel-bounces_at_[hidden] [devel-bounces_at_[hidden]] on
>> behalf of George Bosilca [bosilca_at_[hidden]] Sent: Thursday,
>> October 18, 2012 7:44 AM To: Open MPI Developers
>> Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
>>
>> Check the permissions granted by pam. Look in the /etc/security to
>> check for any type of restrictions.
>>
>> george.
>>
>>
>> On Oct 17, 2012, at 23:30 , "Gutierrez, Samuel K"
>> <samuel_at_[hidden]<mailto:samuel_at_[hidden]>> wrote:
>>
>> Hi,
>>
>> I'm trying to run with CMA support, but process_vm_readv is failing
>> with EPERM when trying to use it as a regular user (everything seems
>> to work fine as root). I've looked around for some solutions, but I
>> can't seem to find what I'm looking for. The documentation states
>> that the target and source processes need to have the same GID and
>> UID to work properly. It appears that they do, so my feeling is that
>> I'm missing something.
>>
>> Any help is greatly appreciated.
>>
>> Thanks,
>>
>> Sam
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]<mailto:devel_at_[hidden]>
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>
> --
> cyeoh_at_[hidden]
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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