[PATCH net-next v2 9/9] netconsole: move find_skb() from netpoll

[Breno Leitao <leitao@debian.org>]

find_skb() is the netconsole-specific entry into the netpoll skb
pool: every other netpoll consumer (bonding, team, vlan, bridge,
macvlan, dsa) builds its own sk_buff and never touches the pool.
With netpoll_send_udp() (its only caller) now living in netconsole,
find_skb() can join it.

Move find_skb() into drivers/net/netconsole.c as a file-static
helper, drop EXPORT_SYMBOL_GPL(find_skb) and remove its prototype
from include/linux/netpoll.h. find_skb() drains TX completions via
netpoll_zap_completion_queue(), which is already exported in the
NETDEV_INTERNAL namespace, so netconsole picks up
MODULE_IMPORT_NS("NETDEV_INTERNAL") to consume it.

The skb pool's lifecycle (np->skb_pool, np->refill_wq, refill_skbs(),
refill_skbs_work_handler(), skb_pool_flush()) stays in netpoll: it
is initialised in __netpoll_setup() and torn down in
__netpoll_cleanup(), both of which remain netpoll's responsibility.
The refill work queued via schedule_work(&np->refill_wq) from the
moved find_skb() runs refill_skbs_work_handler() in netpoll without
any further plumbing.

This is pure code motion: the function body is unchanged and its
sole caller (netpoll_send_udp(), already moved by an earlier patch)
keeps invoking it the same way. Pre-existing concerns about
find_skb() running from NMI/printk context (zap_completion_queue()
re-entry, skb_pool spinlocks, GFP_ATOMIC allocation, fallback skb
sizing vs. MAX_SKB_SIZE, PREEMPT_RT semantics of __kfree_skb()) are
inherited as-is and are not addressed here; they predate this
series and are out of scope. Fixing them is left for follow-up
work.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 28 ++++++++++++++++++++++++++++
 include/linux/netpoll.h  |  1 -
 net/core/netpoll.c       | 28 ----------------------------
 3 files changed, 28 insertions(+), 29 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 48d2670bbdef5..d804d44af87c8 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -50,6 +50,7 @@
 MODULE_AUTHOR("Matt Mackall <mpm@selenic.com>");
 MODULE_DESCRIPTION("Console driver for network interfaces");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("NETDEV_INTERNAL");
 
 #define MAX_PARAM_LENGTH		256
 #define MAX_EXTRADATA_ENTRY_LEN		256
@@ -1653,6 +1654,33 @@ static struct notifier_block netconsole_netdev_notifier = {
 	.notifier_call  = netconsole_netdev_event,
 };
 
+static struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
+{
+	int count = 0;
+	struct sk_buff *skb;
+
+	netpoll_zap_completion_queue();
+repeat:
+
+	skb = alloc_skb(len, GFP_ATOMIC);
+	if (!skb) {
+		skb = skb_dequeue(&np->skb_pool);
+		schedule_work(&np->refill_wq);
+	}
+
+	if (!skb) {
+		if (++count < 10) {
+			netpoll_poll_dev(np->dev);
+			goto repeat;
+		}
+		return NULL;
+	}
+
+	refcount_set(&skb->users, 1);
+	skb_reserve(skb, reserve);
+	return skb;
+}
+
 static void netpoll_udp_checksum(struct netpoll *np, struct sk_buff *skb,
 				 int len)
 {
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index f986f7486cb8c..e4b8f1f91e54b 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -73,7 +73,6 @@ void __netpoll_free(struct netpoll *np);
 void netpoll_cleanup(struct netpoll *np);
 void do_netpoll_cleanup(struct netpoll *np);
 netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb);
-struct sk_buff *find_skb(struct netpoll *np, int len, int reserve);
 void netpoll_zap_completion_queue(void);
 
 #ifdef CONFIG_NETPOLL
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index e4cda0aa4d488..33ab3d827a427 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -265,34 +265,6 @@ void netpoll_zap_completion_queue(void)
 }
 EXPORT_SYMBOL_NS_GPL(netpoll_zap_completion_queue, "NETDEV_INTERNAL");
 
-struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
-{
-	int count = 0;
-	struct sk_buff *skb;
-
-	netpoll_zap_completion_queue();
-repeat:
-
-	skb = alloc_skb(len, GFP_ATOMIC);
-	if (!skb) {
-		skb = skb_dequeue(&np->skb_pool);
-		schedule_work(&np->refill_wq);
-	}
-
-	if (!skb) {
-		if (++count < 10) {
-			netpoll_poll_dev(np->dev);
-			goto repeat;
-		}
-		return NULL;
-	}
-
-	refcount_set(&skb->users, 1);
-	skb_reserve(skb, reserve);
-	return skb;
-}
-EXPORT_SYMBOL_GPL(find_skb);
-
 static int netpoll_owner_active(struct net_device *dev)
 {
 	struct napi_struct *napi;

-- 
2.53.0-Meta