Re: [PATCH net-next] net: flush the softnet backlog in process context

[Eric Dumazet]

On Thu, 2016-08-25 at 07:32 -0700, Eric Dumazet wrote:

> In a future patch, we could change this so that we kick
> flush_all_backlogs() once for all devices, instead of one device at a
> time.
> 
> We would not pass @dev anymore as a parameter and simply look at
> skb->dev->reg_state to decide to remove packets from queues in
> flush_backlog()

This would be something like :

diff --git a/net/core/dev.c b/net/core/dev.c
index 7feae74ca928..793ace2c600f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4293,7 +4293,6 @@ int netif_receive_skb(struct sk_buff *skb)
 EXPORT_SYMBOL(netif_receive_skb);
 
 struct flush_work {
-       struct net_device *dev;
        struct work_struct work;
 };
 
@@ -4303,7 +4302,6 @@ DEFINE_PER_CPU(struct flush_work, flush_works);
 static void flush_backlog(struct work_struct *work)
 {
        struct flush_work *flush = container_of(work, typeof(*flush), work);
-       struct net_device *dev = flush->dev;
        struct sk_buff *skb, *tmp;
        struct softnet_data *sd;
 
@@ -4313,7 +4311,7 @@ static void flush_backlog(struct work_struct *work)
        local_irq_disable();
        rps_lock(sd);
        skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
-               if (skb->dev == dev) {
+               if (skb->dev->reg_state == NETREG_UNREGISTERING) {
                        __skb_unlink(skb, &sd->input_pkt_queue);
                        kfree_skb(skb);
                        input_queue_head_incr(sd);
@@ -4323,7 +4321,7 @@ static void flush_backlog(struct work_struct *work)
        local_irq_enable();
 
        skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
-               if (skb->dev == dev) {
+               if (skb->dev->reg_state == NETREG_UNREGISTERING) {
                        __skb_unlink(skb, &sd->process_queue);
                        kfree_skb(skb);
                        input_queue_head_incr(sd);
@@ -4332,7 +4330,7 @@ static void flush_backlog(struct work_struct *work)
        local_bh_enable();
 }
 
-static void flush_all_backlogs(struct net_device *dev)
+static void flush_all_backlogs(void)
 {
        unsigned int cpu;
 
@@ -4342,7 +4340,6 @@ static void flush_all_backlogs(struct net_device *dev)
                struct flush_work *flush = per_cpu_ptr(&flush_works, cpu);
 
                INIT_WORK(&flush->work, flush_backlog);
-               flush->dev = dev;
                queue_work_on(cpu, system_highpri_wq, &flush->work);
        }
 
@@ -6735,8 +6732,8 @@ static void rollback_registered_many(struct list_head 
*head)
                unlist_netdevice(dev);
 
                dev->reg_state = NETREG_UNREGISTERING;
-               flush_all_backlogs(dev);
        }
+       flush_all_backlogs();
 
        synchronize_net();