mtl/ofi: Do not fail if error CQ is empty

In multi-threaded scenarios, any thread that attempts to read a CQ
when there's a pending error CQ entry gets an -FI_EAVAIL. Without
any serialization here (which is okay, since libfabric will protect
access to critical CQ objects), all threads proceed to read from the
error CQ, but only one thread fetches the entry while others get
-FI_EAGAIN indicating an empty queue, which is not erroneous.

Signed-off-by: Raghu Raja <craghun@amazon.com>
(cherry picked from commit 415dddb9afbed28dc93f65ead867ef5d245d94c4)

ompi/mca/mtl/ofi/mtl_ofi.h

@@ -137,6 +137,17 @@ ompi_mtl_ofi_context_progress(int ctxt_id)
                                 &error,
                                 0);
             if (0 > ret) {
+                /*
+                 * In multi-threaded scenarios, any thread that attempts to read
+                 * a CQ when there's a pending error CQ entry gets an
+                 * -FI_EAVAIL. Without any serialization here (which is okay,
+                 * since libfabric will protect access to critical CQ objects),
+                 * all threads proceed to read from the error CQ, but only one
+                 * thread fetches the entry while others get -FI_EAGAIN
+                 * indicating an empty queue, which is not erroneous.
+                 */
+                if (ret == -FI_EAGAIN)
+                    return count;
                 opal_output(0, "%s:%d: Error returned from fi_cq_readerr: %s(%zd).\n"
                                "*** The Open MPI OFI MTL is aborting the MPI job (via exit(3)).\n",
                                __FILE__, __LINE__, fi_strerror(-ret), ret);