netdev - [PATCH 20/45] net: Use get/put_online_cpus

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Date:	Sun, 23 Jun 2013 19:12:40 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org, laijs@...fujitsu.com
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, sbw@....edu, fweisbec@...il.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	srivatsa.bhat@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	netdev@...r.kernel.org
Subject: [PATCH 20/45] net: Use get/put_online_cpus_atomic() to prevent CPU
 offline

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Duyck <alexander.h.duyck@...el.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Ben Hutchings <bhutchings@...arflare.com>
Cc: netdev@...r.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 net/core/dev.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fc1e289..90519e9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3141,7 +3141,7 @@ int netif_rx(struct sk_buff *skb)
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
 		int cpu;
 
-		preempt_disable();
+		get_online_cpus_atomic();
 		rcu_read_lock();
 
 		cpu = get_rps_cpu(skb->dev, skb, &rflow);
@@ -3151,7 +3151,7 @@ int netif_rx(struct sk_buff *skb)
 		ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 
 		rcu_read_unlock();
-		preempt_enable();
+		put_online_cpus_atomic();
 	} else
 #endif
 	{
@@ -3570,6 +3570,7 @@ int netif_receive_skb(struct sk_buff *skb)
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
 		int cpu, ret;
 
+		get_online_cpus_atomic();
 		rcu_read_lock();
 
 		cpu = get_rps_cpu(skb->dev, skb, &rflow);
@@ -3577,9 +3578,11 @@ int netif_receive_skb(struct sk_buff *skb)
 		if (cpu >= 0) {
 			ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 			rcu_read_unlock();
+			put_online_cpus_atomic();
 			return ret;
 		}
 		rcu_read_unlock();
+		put_online_cpus_atomic();
 	}
 #endif
 	return __netif_receive_skb(skb);
@@ -3957,6 +3960,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 		local_irq_enable();
 
 		/* Send pending IPI's to kick RPS processing on remote cpus. */
+		get_online_cpus_atomic();
 		while (remsd) {
 			struct softnet_data *next = remsd->rps_ipi_next;
 
@@ -3965,6 +3969,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 							   &remsd->csd, 0);
 			remsd = next;
 		}
+		put_online_cpus_atomic();
 	} else
 #endif
 		local_irq_enable();

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