CORTX-33725: Add lock for m0_rpc_bulk buffer(rbulk) (Seagate#2072)

rbulk buffer was not protected under lock in ioreq_fop_dgmode_read().
Added lock which was missing earlier.

Signed-off-by: Yatin Mahajan <yatin.mahajan@seagate.com>

motr/io_req_fop.c

@@ -756,6 +756,7 @@ M0_INTERNAL int ioreq_fop_dgmode_read(struct ioreq_fop *irfop)
 	               ioo_nwxfer, &ioo_bobtype);
 	rbulk = &irfop->irf_iofop.if_rbulk;
 
+	m0_mutex_lock(&rbulk->rb_mutex);
 	m0_tl_for (rpcbulk, &rbulk->rb_buflist, rbuf) {
 
 		index  = rbuf->bb_zerovec.z_index;
@@ -783,10 +784,13 @@ M0_INTERNAL int ioreq_fop_dgmode_read(struct ioreq_fop *irfop)
 			rc = map->pi_ops->pi_dgmode_process(map,
 					irfop->irf_tioreq, &index[seg - cnt],
 					cnt);
-			if (rc != 0)
+			if (rc != 0) {
+				m0_mutex_unlock(&rbulk->rb_mutex);
 				return M0_ERR(rc);
+			}
 		}
 	} m0_tl_endfor;
+	m0_mutex_unlock(&rbulk->rb_mutex);
 	return M0_RC(0);
 }