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

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Date:   Thu, 25 Aug 2016 07:47:36 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Tom Herbert <tom@...bertland.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net-next] net: flush the softnet backlog in process
 context

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();