net: rps: fix cpu unplug

softnet_data.input_pkt_queue is protected by a spinlock that
we must hold when transferring packets from victim queue to an active
one. This is because other cpus could still be trying to enqueue packets
into victim queue.

A second problem is that when we transfert the NAPI poll_list from
victim to current cpu, we absolutely need to special case the percpu
backlog, because we do not want to add complex locking to protect
process_queue : Only owner cpu is allowed to manipulate it, unless cpu
is offline.

Based on initial patch from Prasad Sodagudi & Subash Abhinov
Kasiviswanathan.

This version is better because we do not slow down packet processing,
only make migration safer.

Reported-by: Prasad Sodagudi <psodagud@codeaurora.org>
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 683d493aa1bf2225ac0c029ac403841f7d3c740e..171420e75b03e5b9a020e6d417b72efbed5d5aba 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7072,10 +7072,20 @@ 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);
+       /* Append NAPI poll list from offline CPU, with one exception :
+        * process_backlog() must be called by cpu owning percpu backlog.
+        * We properly handle process_queue & input_pkt_queue later.
+        */
+       while (!list_empty(&oldsd->poll_list)) {
+               struct napi_struct *napi = list_first_entry(&oldsd->poll_list,
+                                                           struct napi_struct,
+                                                           poll_list);
+
+               list_del_init(&napi->poll_list);
+               if (napi->poll == process_backlog)
+                       napi->state = 0;
+               else
+                       ____napi_schedule(sd, napi);
        }
 
        raise_softirq_irqoff(NET_TX_SOFTIRQ);
@@ -7086,7 +7096,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
                netif_rx_internal(skb);
                input_queue_head_incr(oldsd);
        }
-       while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
+       while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
                netif_rx_internal(skb);
                input_queue_head_incr(oldsd);
        }