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

[Adam T. Moody]

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