MTL/OFI: Check threshold number of peers allowed per rank

When the provider does not support FI_REMOTE_CQ_DATA, the OFI tag does not have
sizeof(int) bits for the rank. Therefore, unexpected behavior will occur when
this limit is crossed.

Check the max allowed number of ranks during add_procs() and return if there is
danger of exceeding this threshold.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@intel.com>

ompi/mca/mtl/ofi/mtl_ofi.c

@@ -54,9 +54,22 @@ ompi_mtl_ofi_add_procs(struct mca_mtl_base_module_t *mtl,
     char *ep_names = NULL;
     fi_addr_t *fi_addrs = NULL;
     mca_mtl_ofi_endpoint_t *endpoint = NULL;
+    int num_peers_limit = (1 << ompi_mtl_ofi.num_bits_source_rank) - 1;
 
     namelen = ompi_mtl_ofi.epnamelen;
 
+    /* We cannot add more ranks than available tag bits */
+    if ((false == ompi_mtl_ofi.fi_cq_data) &&
+        OPAL_UNLIKELY(((int) (nprocs + ompi_mtl_ofi.num_peers) > num_peers_limit))) {
+        opal_output(0, "%s:%d: OFI provider: %s does not have enough bits for source rank in its tag.\n"
+                       "Adding more ranks will result in undefined behaviour. Please enable\n"
+                       "FI_REMOTE_CQ_DATA feature in the provider. For more info refer fi_cq(3).\n",
+                       __FILE__, __LINE__, ompi_mtl_ofi.provider_name);
+        fflush(stderr);
+        ret = OMPI_ERROR;
+        goto bail;
+    }
+
     /**
      * Create array of EP names.
      */
@@ -126,6 +139,9 @@ ompi_mtl_ofi_add_procs(struct mca_mtl_base_module_t *mtl,
         procs[i]->proc_endpoints[OMPI_PROC_ENDPOINT_TAG_MTL] = endpoint;
     }
 
+    /* Update global counter of number of procs added to this rank */
+    ompi_mtl_ofi.num_peers += nprocs;
+
     ret = OMPI_SUCCESS;
 
 bail:

ompi/mca/mtl/ofi/mtl_ofi_component.c

@@ -15,7 +15,6 @@
 
 #include "mtl_ofi.h"
 #include "opal/util/argv.h"
-#include "opal/util/show_help.h"
 #include "opal/util/printf.h"
 
 static int ompi_mtl_ofi_component_open(void);
@@ -607,6 +606,7 @@ ompi_mtl_ofi_component_init(bool enable_progress_threads,
 
     /* Update the maximum supported Communicator ID */
     ompi_mtl_ofi.base.mtl_max_contextid = (int)((1ULL << ofi_tag_bits_for_cid) - 1);
+    ompi_mtl_ofi.num_peers = 0;
 
     /**
      * Open fabric
@@ -740,6 +740,8 @@ ompi_mtl_ofi_component_init(bool enable_progress_threads,
         goto error;
     }
 
+    ompi_mtl_ofi.provider_name = strdup(prov->fabric_attr->prov_name);
+
     /**
      * Free providers info since it's not needed anymore.
      */

ompi/mca/mtl/ofi/mtl_ofi_endpoint.h

@@ -41,7 +41,13 @@ typedef struct mca_mtl_ofi_endpoint_t  mca_mtl_ofi_endpoint_t;
 static inline mca_mtl_ofi_endpoint_t *ompi_mtl_ofi_get_endpoint (struct mca_mtl_base_module_t* mtl, ompi_proc_t *ompi_proc)
 {
     if (OPAL_UNLIKELY(NULL == ompi_proc->proc_endpoints[OMPI_PROC_ENDPOINT_TAG_MTL])) {
-        ompi_mtl_ofi_add_procs(mtl, 1, &ompi_proc);
+        if (OPAL_UNLIKELY(OMPI_SUCCESS != ompi_mtl_ofi_add_procs(mtl, 1, &ompi_proc))) {
+            /* Fatal error. exit() out */
+            opal_output(0, "%s:%d: *** The Open MPI OFI MTL is aborting the MPI job (via exit(3)).\n",
+                           __FILE__, __LINE__);
+            fflush(stderr);
+            exit(1);
+        }
     }
 
     return ompi_proc->proc_endpoints[OMPI_PROC_ENDPOINT_TAG_MTL];

ompi/mca/mtl/ofi/mtl_ofi_types.h

@@ -43,7 +43,7 @@ typedef struct mca_mtl_ofi_module_t {
     /** "Any source" address */
     fi_addr_t any_addr;
 
-    /** Optional user-specified OFI provider name */
+    /** OFI provider name */
     char *provider_name;
 
     /** Maximum inject size */
@@ -61,6 +61,7 @@ typedef struct mca_mtl_ofi_module_t {
     unsigned long long source_rank_mask;
     unsigned long long mpi_tag_mask;
     int num_bits_mpi_tag;
+    int num_peers;
 
     /** Synchronous protocol tag bits */
     unsigned long long sync_send;