net: extract napi poll functionality to __napi_poll()

This commit introduces a new function __napi_poll() which does the main
logic of the existing napi_poll() function, and will be called by other
functions in later commits.
This idea and implementation is done by Felix Fietkau <nbd@nbd.name> and
is proposed as part of the patch to move napi work to work_queue
context.
This commit by itself is a code restructure.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Wei Wang <weiwan@google.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -6776,15 +6776,10 @@ void __netif_napi_del(struct napi_struct *napi)
 }
 EXPORT_SYMBOL(__netif_napi_del);
 
-static int napi_poll(struct napi_struct *n, struct list_head *repoll)
+static int __napi_poll(struct napi_struct *n, bool *repoll)
 {
-	void *have;
 	int work, weight;
 
-	list_del_init(&n->poll_list);
-
-	have = netpoll_poll_lock(n);
-
 	weight = n->weight;
 
 	/* This NAPI_STATE_SCHED test is for avoiding a race
@@ -6804,7 +6799,7 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 			    n->poll, work, weight);
 
 	if (likely(work < weight))
-		goto out_unlock;
+		return work;
 
 	/* Drivers must not modify the NAPI state if they
 	 * consume the entire weight.  In such cases this code
@@ -6813,7 +6808,7 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 	 */
 	if (unlikely(napi_disable_pending(n))) {
 		napi_complete(n);
-		goto out_unlock;
+		return work;
 	}
 
 	/* The NAPI context has more processing work, but busy-polling
@@ -6826,7 +6821,7 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 			 */
 			napi_schedule(n);
 		}
-		goto out_unlock;
+		return work;
 	}
 
 	if (n->gro_bitmask) {
@@ -6844,12 +6839,29 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 	if (unlikely(!list_empty(&n->poll_list))) {
 		pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
 			     n->dev ? n->dev->name : "backlog");
-		goto out_unlock;
+		return work;
 	}
 
-	list_add_tail(&n->poll_list, repoll);
+	*repoll = true;
+
+	return work;
+}
+
+static int napi_poll(struct napi_struct *n, struct list_head *repoll)
+{
+	bool do_repoll = false;
+	void *have;
+	int work;
+
+	list_del_init(&n->poll_list);
+
+	have = netpoll_poll_lock(n);
+
+	work = __napi_poll(n, &do_repoll);
+
+	if (do_repoll)
+		list_add_tail(&n->poll_list, repoll);
 
-out_unlock:
 	netpoll_poll_unlock(have);
 
 	return work;