[Bug 9106] ip neigh flush dev eth0 is hanging

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Ubuntu | linux





------- Additional Comments From herbert at linuxhacker.at  2005-08-02 09:58 UTC -------
If this bug is not a kernel problem, then this could be a iproute problem. I
found this workaround.


**Patch for iproute**

  Another possible solution is a change of iproute, to avoid the loop situation.
The source code for flush looks like::

              for (;;) {
                      if (rtnl_wilddump_request(&rth, filter.family,
RTM_GETNEIGH) < 0) {
                              perror("Cannot send dump request");
                              exit(1);
                      }
                      filter.flushed = 0;
                      if (rtnl_dump_filter(&rth, print_neigh, stdout, NULL,
NULL) < 0) {
                              fprintf(stderr, "Flush terminated\n");
                              exit(1);
                      }
                      if (filter.flushed == 0) {
                              if (round == 0) {
                                      fprintf(stderr, "Nothing to flush.\n");
                              } else if (show_stats)
                                      printf("*** Flush is complete after %d
round%s ***\n", round, round>1?"s":"");
                              fflush(stdout);
                              return 0;
                      }
                      round++;
                      if (flush_update() < 0)
                              exit(1);
                      if (show_stats) {
                              printf("\n*** Round %d, deleting %d entries
***\n", round, filter.flushed);
                              fflush(stdout);
                      }
              }
      }


  There is no way out of the loop, if the arp entry cannot be flushed. The 'for
(;;)' construction can be found in other .c files. In iproute.c there is a exit
construction like the following patch::

    --- ip/ipneigh.c.orig   2005-07-26 16:10:40.850647298 +0200
    +++ ip/ipneigh.c        2005-07-26 16:11:09.302486025 +0200
    @@ -410,6 +410,7 @@
                    filter.flushe = sizeof(flushb);
                    filter.rth = &rth;
                    filter.state &= ~NUD_FAILED;
    +               time_t start = time(0);

                    for (;;) {
                            if (rtnl_wilddump_request(&rth, filter.family,
RTM_GETNEIGH) < 0) {
    @@ -432,6 +433,12 @@
                            round++;
                            if (flush_update() < 0)
                                    exit(1);
    +                       if (time(0) - start > 30) {
    +                               printf("\n*** Flush not completed after %ld
seconds, %d entries remain ***\n",
    +                              time(0) - start, filter.flushed);
    +                               exit(1);
    +                       }
    +
                            if (show_stats) {
                                    printf("\n*** Round %d, deleting %d entries
***\n", round, filter.flushed);
                                    fflush(stdout);


  This is not ideal, but avoid a endless loop. The output of 'ip -s -4 neigh
flush dev eth1' looks like::

    ... 

    *** Round 57934, deleting 1 entries ***

    *** Round 57935, deleting 1 entries ***

    *** Round 57936, deleting 1 entries ***

    *** Flush not completed after 31 seconds, 1 entries remain ***

  The disadvantage of this solution is the 100% CPU consum for 30 seconds.


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