target/linux/mvebu/patches-4.4/038-net-mvneta-Fix-the-CPU-choice-in-mvneta_percpu_elect.patch

   1 From: Gregory CLEMENT <gregory.clement@free-electrons.com>
   2 Date: Thu, 4 Feb 2016 22:09:24 +0100
   3 Subject: [PATCH] net: mvneta: Fix the CPU choice in mvneta_percpu_elect
   4
   5 When passing to the management of multiple RX queue, the
   6 mvneta_percpu_elect function was broken. The use of the modulo can lead
   7 to elect the wrong cpu. For example with rxq_def=2, if the CPU 2 goes
   8 offline and then online, we ended with the third RX queue activated in
   9 the same time on CPU 0 and CPU2, which lead to a kernel crash.
  10
  11 With this fix, we don't try to get "the closer" CPU if the default CPU is
  12 gone, now we just use CPU 0 which always be there. Thanks to this, the
  13 code becomes more readable, easier to maintain and more predicable.
  14
  15 Cc: stable@vger.kernel.org
  16 Fixes: 2dcf75e2793c ("net: mvneta: Associate RX queues with each CPU")
  17 Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
  18 Signed-off-by: David S. Miller <davem@davemloft.net>
  19 ---
  20
  21 --- a/drivers/net/ethernet/marvell/mvneta.c
  22 +++ b/drivers/net/ethernet/marvell/mvneta.c
  23 @@ -2851,9 +2851,14 @@ static void mvneta_percpu_disable(void *
  24
  25  static void mvneta_percpu_elect(struct mvneta_port *pp)
  26  {
  27 -       int online_cpu_idx, max_cpu, cpu, i = 0;
  28 +       int elected_cpu = 0, max_cpu, cpu, i = 0;
  29 +
  30 +       /* Use the cpu associated to the rxq when it is online, in all
  31 +        * the other cases, use the cpu 0 which can't be offline.
  32 +        */
  33 +       if (cpu_online(pp->rxq_def))
  34 +               elected_cpu = pp->rxq_def;
  35
  36 -       online_cpu_idx = pp->rxq_def % num_online_cpus();
  37         max_cpu = num_present_cpus();
  38
  39         for_each_online_cpu(cpu) {
  40 @@ -2864,7 +2869,7 @@ static void mvneta_percpu_elect(struct m
  41                         if ((rxq % max_cpu) == cpu)
  42                                 rxq_map |= MVNETA_CPU_RXQ_ACCESS(rxq);
  43
  44 -               if (i == online_cpu_idx)
  45 +               if (cpu == elected_cpu)
  46                         /* Map the default receive queue queue to the
  47                          * elected CPU
  48                          */
  49 @@ -2875,7 +2880,7 @@ static void mvneta_percpu_elect(struct m
  50                  * the CPU bound to the default RX queue
  51                  */
  52                 if (txq_number == 1)
  53 -                       txq_map = (i == online_cpu_idx) ?
  54 +                       txq_map = (cpu == elected_cpu) ?
  55                                 MVNETA_CPU_TXQ_ACCESS(1) : 0;
  56                 else
  57                         txq_map = mvreg_read(pp, MVNETA_CPU_MAP(cpu)) &