Subject: net: Remove preemption disabling in netif_rx()
From: Priyanka Jain <Priyanka.Jain@freescale.com>
Date: Thu, 17 May 2012 09:35:11 +0530
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

1)enqueue_to_backlog() (called from netif_rx) should be
  bind to a particluar CPU. This can be achieved by
  disabling migration. No need to disable preemption

2)Fixes crash "BUG: scheduling while atomic: ksoftirqd"
  in case of RT.
  If preemption is disabled, enqueue_to_backog() is called
  in atomic context. And if backlog exceeds its count,
  kfree_skb() is called. But in RT, kfree_skb() might
  gets scheduled out, so it expects non atomic context.

3)When CONFIG_PREEMPT_RT_FULL is not defined,
 migrate_enable(), migrate_disable() maps to
 preempt_enable() and preempt_disable(), so no
 change in functionality in case of non-RT.

-Replace preempt_enable(), preempt_disable() with
 migrate_enable(), migrate_disable() respectively
-Replace get_cpu(), put_cpu() with get_cpu_light(),
 put_cpu_light() respectively

Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Acked-by: Rajan Srivastava <Rajan.Srivastava@freescale.com>
Cc: <rostedt@goodmis.orgn>
Link: http://lkml.kernel.org/r/1337227511-2271-1-git-send-email-Priyanka.Jain@freescale.com

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 Testing: Tested successfully on p4080ds(8-core SMP system)  

 net/core/dev.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3790,7 +3790,7 @@ static int netif_rx_internal(struct sk_b
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
 		int cpu;
 
-		preempt_disable();
+		migrate_disable();
 		rcu_read_lock();
 
 		cpu = get_rps_cpu(skb->dev, skb, &rflow);
@@ -3800,13 +3800,13 @@ static int netif_rx_internal(struct sk_b
 		ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 
 		rcu_read_unlock();
-		preempt_enable();
+		migrate_enable();
 	} else
 #endif
 	{
 		unsigned int qtail;
-		ret = enqueue_to_backlog(skb, get_cpu(), &qtail);
-		put_cpu();
+		ret = enqueue_to_backlog(skb, get_cpu_light(), &qtail);
+		put_cpu_light();
 	}
 	return ret;
 }
