Re: [PATCH net-next 20/27] sctp: add rfc6525 section 5.2.2

On Sun, Jan 1, 2017 at 8:02 PM, kbuild test robot [off-list ref] wrote:

Hi Xin,

[auto build test WARNING on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Xin-Long/sctp-implement-rfc6525-sctp-stream-reconf/20170101-192844
config: x86_64-randconfig-x015-201701 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   net/sctp/stream.c: In function 'sctp_process_strreset_outreq':

quoted

quoted

net/sctp/stream.c:140:9: warning: 'str_p' may be used uninitialized in this function [-Wmaybe-uninitialized]

     *evp = sctp_ulpevent_make_stream_reset_event(asoc,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      flags | SCTP_STREAM_RESET_OUTGOING_SSN, nums, str_p,
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      GFP_ATOMIC);
      ~~~~~~~~~~~

This warning is actually safe, as only when nums is NULL, str_p is
uninitialized, and in sctp_ulpevent_make_stream_reset_event(), if nums
is null, str_p wouldn't be really used.

vim +/str_p +140 net/sctp/stream.c

   124                          if (str_p[i] >= asoc->streamincnt) {
   125                                  result = SCTP_STRRESET_ERR_WRONG_SSN;
   126                                  goto out;
   127                          }
   128                  }
   129
   130                  str_p = outreq->list_of_streams;
   131                  for (i = 0; i < nums; i++, str_p++)
   132                          asoc->streamin[*str_p].ssn = 0;
   133          } else {
   134                  for (i = 0; i < asoc->streamincnt; i++)
   135                          asoc->streamin[i].ssn = 0;
   136          }
   137
   138          result = SCTP_STRRESET_PERFORMED;
   139
 > 140          *evp = sctp_ulpevent_make_stream_reset_event(asoc,
   141                  flags | SCTP_STREAM_RESET_OUTGOING_SSN, nums, str_p,
   142                  GFP_ATOMIC);
   143
   144  out:
   145          return sctp_make_strreset_resp(asoc, result, request_seq);
   146  }

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