net: cpu offline cause napi stall

Frank Blaschka reported :
<quote>
  During heavy network load we turn off/on cpus.
  Sometimes this causes a stall on the network device.
  Digging into the dump I found out following:

  napi is scheduled but does not run. From the I/O buffers
  and the napi state I see napi/rx_softirq processing has stopped
  because the budget was reached. napi stays in the
  softnet_data poll_list and the rx_softirq was raised again.

  I assume at this time the cpu offline comes in,
  the rx softirq is raised/moved to another cpu but napi stays in the
  poll_list of the softnet_data of the now offline cpu.

  Reviewing dev_cpu_callback (net/core/dev.c) I did not find the
  poll_list is transfered to the new cpu.
</quote>

This patch is a straightforward implementation of Frank suggestion :

Transfert poll_list and trigger NET_RX_SOFTIRQ on new cpu.

Reported-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 1af6cb27f67a..a54c9f87ddbb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6178,6 +6178,11 @@ static int dev_cpu_callback(struct notifier_block *nfb,
                 oldsd->output_queue = NULL;
                 oldsd->output_queue_tailp = &oldsd->output_queue;
         }
+        /* Append NAPI poll list from offline CPU. */
+        if (!list_empty(&oldsd->poll_list)) {
+                list_splice_init(&oldsd->poll_list, &sd->poll_list);
+                raise_softirq_irqoff(NET_RX_SOFTIRQ);
+        }
 
         raise_softirq_irqoff(NET_TX_SOFTIRQ);
         local_irq_enable();