net: do not provide hard irq safety for sd->defer_lock

kfree_skb() can be called from hard irq handlers,
but skb_attempt_defer_free() is meant to be used
from process or BH contexts, and skb_defer_free_flush()
is meant to be called from BH contexts.

Not having to mask hard irq can save some cycles.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

net/core/dev.c

@@ -6632,11 +6632,11 @@ static void skb_defer_free_flush(struct softnet_data *sd)
 	if (!READ_ONCE(sd->defer_list))
 		return;
 
-	spin_lock_irq(&sd->defer_lock);
+	spin_lock(&sd->defer_lock);
 	skb = sd->defer_list;
 	sd->defer_list = NULL;
 	sd->defer_count = 0;
-	spin_unlock_irq(&sd->defer_lock);
+	spin_unlock(&sd->defer_lock);
 
 	while (skb != NULL) {
 		next = skb->next;

net/core/skbuff.c

@@ -6870,7 +6870,6 @@ void skb_attempt_defer_free(struct sk_buff *skb)
 {
 	int cpu = skb->alloc_cpu;
 	struct softnet_data *sd;
-	unsigned long flags;
 	unsigned int defer_max;
 	bool kick;
 
@@ -6889,7 +6888,7 @@ nodefer:	__kfree_skb(skb);
 	if (READ_ONCE(sd->defer_count) >= defer_max)
 		goto nodefer;
 
-	spin_lock_irqsave(&sd->defer_lock, flags);
+	spin_lock_bh(&sd->defer_lock);
 	/* Send an IPI every time queue reaches half capacity. */
 	kick = sd->defer_count == (defer_max >> 1);
 	/* Paired with the READ_ONCE() few lines above */
@@ -6898,7 +6897,7 @@ nodefer:	__kfree_skb(skb);
 	skb->next = sd->defer_list;
 	/* Paired with READ_ONCE() in skb_defer_free_flush() */
 	WRITE_ONCE(sd->defer_list, skb);
-	spin_unlock_irqrestore(&sd->defer_lock, flags);
+	spin_unlock_bh(&sd->defer_lock);
 
 	/* Make sure to trigger NET_RX_SOFTIRQ on the remote CPU
 	 * if we are unlucky enough (this seems very unlikely).