The netpoll subsystem maintains a pool of 32 pre-allocated SKBs per
instance, but these SKBs are not freed when the netpoll user is brought
down. This leads to memory waste as these buffers remain allocated but
unused.

Add skb_pool_flush() to properly clean up these SKBs when netconsole is
terminated, improving memory efficiency.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/core/netpoll.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 719c9aae845fbeb6f5b53a2bef675d3cb8cd44a7..498cc38073a3dc9f829f74f254bc70b26ef3856c 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -531,6 +531,22 @@ static int netpoll_parse_ip_addr(const char *str, union inet_addr *addr)
 	return -1;
 }
 
+static void skb_pool_flush(struct netpoll *np)
+{
+	struct sk_buff_head *skb_pool;
+	struct sk_buff *skb;
+	unsigned long flags;
+
+	skb_pool = &np->skb_pool;
+
+	spin_lock_irqsave(&skb_pool->lock, flags);
+	while (skb_pool->qlen > 0) {
+		skb = __skb_dequeue(skb_pool);
+		kfree_skb(skb);
+	}
+	spin_unlock_irqrestore(&skb_pool->lock, flags);
+}
+
 int netpoll_parse_options(struct netpoll *np, char *opt)
 {
 	char *cur=opt, *delim;
@@ -779,10 +795,12 @@ int netpoll_setup(struct netpoll *np)
 
 	err = __netpoll_setup(np, ndev);
 	if (err)
-		goto put;
+		goto flush;
 	rtnl_unlock();
 	return 0;
 
+flush:
+	skb_pool_flush(np);
 put:
 	DEBUG_NET_WARN_ON_ONCE(np->dev);
 	if (ip_overwritten)
@@ -830,6 +848,8 @@ void __netpoll_cleanup(struct netpoll *np)
 		call_rcu(&npinfo->rcu, rcu_cleanup_netpoll_info);
 	} else
 		RCU_INIT_POINTER(np->dev->npinfo, NULL);
+
+	skb_pool_flush(np);
 }
 EXPORT_SYMBOL_GPL(__netpoll_cleanup);
 

-- 
2.43.5

On Thu, 07 Nov 2024 07:57:07 -0800 Breno Leitao wrote:
> +static void skb_pool_flush(struct netpoll *np)
> +{
> +	struct sk_buff_head *skb_pool;
> +	struct sk_buff *skb;
> +	unsigned long flags;
> +
> +	skb_pool = &np->skb_pool;
> +
> +	spin_lock_irqsave(&skb_pool->lock, flags);
> +	while (skb_pool->qlen > 0) {
> +		skb = __skb_dequeue(skb_pool);
> +		kfree_skb(skb);
> +	}
> +	spin_unlock_irqrestore(&skb_pool->lock, flags);

 skb_queue_purge_reason(... SKB_CONSUMED)

should be able to replace the loop