net: dev: Remove preempt_disable() and get_cpu() in netif_rx_internal().

The preempt_disable() () section was introduced in commit
    cece194 ("net: disable preemption before call smp_processor_id()")

and adds it in case this function is invoked from preemtible context and
because get_cpu() later on as been added.

The get_cpu() usage was added in commit
    b0e28f1 ("net: netif_rx() must disable preemption")

because ip_dev_loopback_xmit() invoked netif_rx() with enabled preemption
causing a warning in smp_processor_id(). The function netif_rx() should
only be invoked from an interrupt context which implies disabled
preemption. The commit
   e30b38c ("ip: Fix ip_dev_loopback_xmit()")

was addressing this and replaced netif_rx() with in netif_rx_ni() in
ip_dev_loopback_xmit().

Based on the discussion on the list, the former patch (b0e28f1)
should not have been applied only the latter (e30b38c).

Remove get_cpu() and preempt_disable() since the function is supposed to
be invoked from context with stable per-CPU pointers. Bottom halves have
to be disabled at this point because the function may raise softirqs
which need to be processed.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Reviewed-by: Toke Høiland-Jørgensen <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Sebastian Andrzej Siewior

net/core/dev.c

@@ -4796,7 +4796,6 @@ static int netif_rx_internal(struct sk_buff *skb)
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
 		int cpu;
 
-		preempt_disable();
 		rcu_read_lock();
 
 		cpu = get_rps_cpu(skb->dev, skb, &rflow);
@@ -4806,14 +4805,12 @@ static int netif_rx_internal(struct sk_buff *skb)
 		ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 
 		rcu_read_unlock();
-		preempt_enable();
 	} else
 #endif
 	{
 		unsigned int qtail;
 
-		ret = enqueue_to_backlog(skb, get_cpu(), &qtail);
-		put_cpu();
+		ret = enqueue_to_backlog(skb, smp_processor_id(), &qtail);
 	}
 	return ret;
 }