netdev - [PATCH net-next] net: flush

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Message-ID: <20250204144825.316785-1-edumazet@google.com>
Date: Tue,  4 Feb 2025 14:48:25 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Simon Horman <horms@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] net: flush_backlog() small changes

Add READ_ONCE() around reads of skb->dev->reg_state, because
this field can be changed from other threads/cpus.

Instead of calling dev_kfree_skb_irq() and kfree_skb()
while interrupts are masked and locks held,
use a temporary list and use __skb_queue_purge_reason()

Use SKB_DROP_REASON_DEV_READY drop reason to better
describe why these skbs are dropped.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index c0021cbd28fc11e4c4eb6184d98a2505fa674871..cd31e78a7d8a2229e3dc17d08bb638f862148823 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6119,16 +6119,18 @@ EXPORT_SYMBOL(netif_receive_skb_list);
 static void flush_backlog(struct work_struct *work)
 {
 	struct sk_buff *skb, *tmp;
+	struct sk_buff_head list;
 	struct softnet_data *sd;
 
+	__skb_queue_head_init(&list);
 	local_bh_disable();
 	sd = this_cpu_ptr(&softnet_data);
 
 	backlog_lock_irq_disable(sd);
 	skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
-		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
+		if (READ_ONCE(skb->dev->reg_state) == NETREG_UNREGISTERING) {
 			__skb_unlink(skb, &sd->input_pkt_queue);
-			dev_kfree_skb_irq(skb);
+			__skb_queue_tail(&list, skb);
 			rps_input_queue_head_incr(sd);
 		}
 	}
@@ -6136,14 +6138,16 @@ static void flush_backlog(struct work_struct *work)
 
 	local_lock_nested_bh(&softnet_data.process_queue_bh_lock);
 	skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
-		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
+		if (READ_ONCE(skb->dev->reg_state) == NETREG_UNREGISTERING) {
 			__skb_unlink(skb, &sd->process_queue);
-			kfree_skb(skb);
+			__skb_queue_tail(&list, skb);
 			rps_input_queue_head_incr(sd);
 		}
 	}
 	local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);
 	local_bh_enable();
+
+	__skb_queue_purge_reason(&list, SKB_DROP_REASON_DEV_READY);
 }
 
 static bool flush_required(int cpu)
-- 
2.48.1.362.g079036d154-goog