[bug report] IB/hfi1: Eliminate allocation while atomic

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Don Hiatt,

The patch f8195f3b14a0: "IB/hfi1: Eliminate allocation while atomic"
from Oct 9, 2017, leads to the following static checker warning:

	drivers/infiniband/hw/hfi1/verbs.c:824 build_verbs_tx_desc()
	error: doing dma on the stack (trail_buf)

drivers/infiniband/hw/hfi1/verbs.c
   147  /* Length of buffer to create verbs txreq cache name */
   148  #define TXREQ_NAME_LEN 24
   149  
   150  /* 16B trailing buffer */
   151  static const u8 trail_buf[MAX_16B_PADDING];
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^

This used to be actually allocated on the stack but now it's here.  I
believe this is still a problem.  It's not a problem for most people at
runtime, but it's technically a bug.  And I believe that soon we will
add a check in dma_map_single() which will generate a warning.

   152  
   153  static uint wss_threshold = 80;

[ snip ]

   801          } else {
   802                  ret = sdma_txinit_ahg(
   803                          &tx->txreq,
   804                          ahg_info->tx_flags,
   805                          length,
   806                          ahg_info->ahgidx,
   807                          ahg_info->ahgcount,
   808                          ahg_info->ahgdesc,
   809                          hdrbytes,
   810                          verbs_sdma_complete);
   811                  if (ret)
   812                          goto bail_txadd;
   813          }
   814          /* add the ulp payload - if any. tx->ss can be NULL for acks */
   815          if (tx->ss) {
   816                  ret = build_verbs_ulp_payload(sde, length, tx);
   817                  if (ret)
   818                          goto bail_txadd;
   819          }
   820  
   821          /* add icrc, lt byte, and padding to flit */
   822          if (extra_bytes)
   823                  ret = sdma_txadd_kvaddr(sde->dd, &tx->txreq,
   824                                          (void *)trail_buf, extra_bytes);
                                                        ^^^^^^^^^
This has to be DMAable memory.

   825  
   826  bail_txadd:
   827          return ret;
   828  }


regards,
dan carpenter