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Subject: Re: [OMPI devel] Cross Memory Attach: What am I Missing?
From: Christopher Yeoh (cyeoh_at_[hidden])
Date: 2012-10-20 07:13:38


Hi Sam,

On Fri, 19 Oct 2012 19:30:16 +0000
"Gutierrez, Samuel K" <samuel_at_[hidden]> wrote:
>
> Thanks for all the info. Below is what can go into the FAQ. Any
> suggestions?
>

Sounds good. One thing that might be worth adding is a suggestion to
look at SE Linux as well if the ptrace_scope setting doesn't work. I
don't know the details but I think Fedora might now disable ptrace by
default using an SE Linux setting.

Regards,

Chris

> 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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