Subject: [PATCH 4/4] net: Rename rps_lock to backlog_lock.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Sat, 9 Mar 2024 10:05:12 +0100

The rps_lock.*() functions use the inner lock of a sk_buff_head for
locking. This lock is used if RPS is enabled, otherwise the list is
accessed lockless and disabling interrupts is enough for the
synchronisation because it is only accessed CPU local. Not only the list
is protected but also the NAPI state protected.
With the addition of backlog threads, the lock is also needed because of
the cross CPU access even without RPS. The clean up of the defer_list
list is also done via backlog threads (if enabled).

It has been suggested to rename the locking function since it is no
longer just RPS.

Rename the rps_lock*() functions to backlog_lock*().

Suggested-by: Jakub Kicinski <[email-masked]>
Acked-by: Jakub Kicinski <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 net/core/dev.c |   34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

Index: linux-6.8.2-rt10/net/core/dev.c
===================================================================
--- linux-6.8.2-rt10.orig/net/core/dev.c
+++ linux-6.8.2-rt10/net/core/dev.c
@@ -242,8 +242,8 @@ static bool use_backlog_threads(void)
 
 #endif
 
-static inline void rps_lock_irqsave(struct softnet_data *sd,
-				    unsigned long *flags)
+static inline void backlog_lock_irq_save(struct softnet_data *sd,
+					 unsigned long *flags)
 {
 	if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads())
 		spin_lock_irqsave(&sd->input_pkt_queue.lock, *flags);
@@ -251,7 +251,7 @@ static inline void rps_lock_irqsave(stru
 		local_irq_save(*flags);
 }
 
-static inline void rps_lock_irq_disable(struct softnet_data *sd)
+static inline void backlog_lock_irq_disable(struct softnet_data *sd)
 {
 	if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads())
 		spin_lock_irq(&sd->input_pkt_queue.lock);
@@ -259,8 +259,8 @@ static inline void rps_lock_irq_disable(
 		local_irq_disable();
 }
 
-static inline void rps_unlock_irq_restore(struct softnet_data *sd,
-					  unsigned long *flags)
+static inline void backlog_unlock_irq_restore(struct softnet_data *sd,
+					      unsigned long *flags)
 {
 	if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads())
 		spin_unlock_irqrestore(&sd->input_pkt_queue.lock, *flags);
@@ -268,7 +268,7 @@ static inline void rps_unlock_irq_restor
 		local_irq_restore(*flags);
 }
 
-static inline void rps_unlock_irq_enable(struct softnet_data *sd)
+static inline void backlog_unlock_irq_enable(struct softnet_data *sd)
 {
 	if (IS_ENABLED(CONFIG_RPS) || use_backlog_threads())
 		spin_unlock_irq(&sd->input_pkt_queue.lock);
@@ -4758,12 +4758,12 @@ void kick_defer_list_purge(struct softne
 	unsigned long flags;
 
 	if (use_backlog_threads()) {
-		rps_lock_irqsave(sd, &flags);
+		backlog_lock_irq_save(sd, &flags);
 
 		if (!__test_and_set_bit(NAPI_STATE_SCHED, &sd->backlog.state))
 			__napi_schedule_irqoff(&sd->backlog);
 
-		rps_unlock_irq_restore(sd, &flags);
+		backlog_unlock_irq_restore(sd, &flags);
 
 	} else if (!cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) {
 		smp_call_function_single_async(cpu, &sd->defer_csd);
@@ -4825,7 +4825,7 @@ static int enqueue_to_backlog(struct sk_
 	reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	sd = &per_cpu(softnet_data, cpu);
 
-	rps_lock_irqsave(sd, &flags);
+	backlog_lock_irq_save(sd, &flags);
 	if (!netif_running(skb->dev))
 		goto drop;
 	qlen = skb_queue_len(&sd->input_pkt_queue);
@@ -4834,7 +4834,7 @@ static int enqueue_to_backlog(struct sk_
 enqueue:
 			__skb_queue_tail(&sd->input_pkt_queue, skb);
 			input_queue_tail_incr_save(sd, qtail);
-			rps_unlock_irq_restore(sd, &flags);
+			backlog_unlock_irq_restore(sd, &flags);
 			return NET_RX_SUCCESS;
 		}
 
@@ -4849,7 +4849,7 @@ enqueue:
 
 drop:
 	sd->dropped++;
-	rps_unlock_irq_restore(sd, &flags);
+	backlog_unlock_irq_restore(sd, &flags);
 
 	dev_core_stats_rx_dropped_inc(skb->dev);
 	kfree_skb_reason(skb, reason);
@@ -5880,7 +5880,7 @@ static void flush_backlog(struct work_st
 	local_bh_disable();
 	sd = this_cpu_ptr(&softnet_data);
 
-	rps_lock_irq_disable(sd);
+	backlog_lock_irq_disable(sd);
 	skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
 		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
 			__skb_unlink(skb, &sd->input_pkt_queue);
@@ -5888,7 +5888,7 @@ static void flush_backlog(struct work_st
 			input_queue_head_incr(sd);
 		}
 	}
-	rps_unlock_irq_enable(sd);
+	backlog_unlock_irq_enable(sd);
 
 	skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
 		if (skb->dev->reg_state == NETREG_UNREGISTERING) {
@@ -5906,14 +5906,14 @@ static bool flush_required(int cpu)
 	struct softnet_data *sd = &per_cpu(softnet_data, cpu);
 	bool do_flush;
 
-	rps_lock_irq_disable(sd);
+	backlog_lock_irq_disable(sd);
 
 	/* as insertion into process_queue happens with the rps lock held,
 	 * process_queue access may race only with dequeue
 	 */
 	do_flush = !skb_queue_empty(&sd->input_pkt_queue) ||
 		   !skb_queue_empty_lockless(&sd->process_queue);
-	rps_unlock_irq_enable(sd);
+	backlog_unlock_irq_enable(sd);
 
 	return do_flush;
 #endif
@@ -6028,7 +6028,7 @@ static int process_backlog(struct napi_s
 
 		}
 
-		rps_lock_irq_disable(sd);
+		backlog_lock_irq_disable(sd);
 		if (skb_queue_empty(&sd->input_pkt_queue)) {
 			/*
 			 * Inline a custom version of __napi_complete().
@@ -6044,7 +6044,7 @@ static int process_backlog(struct napi_s
 			skb_queue_splice_tail_init(&sd->input_pkt_queue,
 						   &sd->process_queue);
 		}
-		rps_unlock_irq_enable(sd);
+		backlog_unlock_irq_enable(sd);
 	}
 
 	return work;