[mvapich-discuss] CMA fails if executable's read permission bit is disabled

[Hari Subramoni]

Hi Adam,

Thanks for the report. We will look into it and get back to you. You can
disable CMA at runtime by setting MV2_SMP_USE_CMA=0. Can you please try
this while we work on a patch?

Regards,
Hari.

On Thu, Nov 10, 2016 at 4:42 PM, Adam T. Moody <moody20 at llnl.gov> wrote:

> Hello MVAPICH team,
> We have an application that disables its read permission bit (i.e., chmod
> -r).  If we run this app with MV2-2.2 on gen2 using at least two procs on
> one node, we get the following error:
>
> [MPIDI_CH3I_SMP_init] CMA is not available. Set MV2_SMP_USE_CMA=0 to
> disable CMA.
> Fatal error in MPI_Init:
> Other MPI error, error stack:
> MPIR_Init_thread(514)....:
> MPID_Init(365)...........: channel initialization failed
> MPIDI_CH3_Init(404)......:
> MPIDI_CH3I_SMP_Init(2132): process_vm_readv: Operation not permitted
>
> If we enable the read bit (chmod +r) it works.
>
> It seems that something goes wrong when read permission is disabled when
> using process_vm_writev() from check_cma_usability() in
> src/mpid/ch3/channels/mrail/src/rdma/ch3_smp_progress.c.
>
> This should reproduce with any simple MPI job.
>
> Can we get CMA to work when disabling the read bit like this? That's an
> important requirement for this application.
>
> Otherwise, could we patch MV2 so that it dynamically disables CMA instead
> of failing with the error?
> Thanks,
> -Adam
>
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