Subject: [RFC PATCH net-next] packet: fix using smp_processor_id() in preemptible code

From: Li Zhong <[email-masked]>
Date: Thu, 12 Dec 2013 14:10:04 +0800

This patches tries to fix the following warning on next-1211 by
replacing smp_processor_id() with raw_smp_processor_id(). 

Also, it seems that we could move skb_set_queue_mapping() into
packet_pick_tx_queue(), so we avoid calling it one more time
unnecessarily if we are going into the normal dev_queue_xmit() code
path. 

[   11.120893] BUG: using smp_processor_id() in preemptible [00000000] code: arping/3510
[   11.120913] caller is .packet_sendmsg+0xc14/0xe68
[   11.120920] CPU: 13 PID: 3510 Comm: arping Not tainted 3.13.0-rc3-next-20131211-dirty #1
[   11.120926] Call Trace:
[   11.120932] [c0000001f803f6f0] [c0000000000138dc] .show_stack+0x110/0x25c (unreliable)
[   11.120942] [c0000001f803f7e0] [c00000000083dd24] .dump_stack+0xa0/0x37c
[   11.120951] [c0000001f803f870] [c000000000493fd4] .debug_smp_processor_id+0xfc/0x12c
[   11.120959] [c0000001f803f900] [c0000000007eba78] .packet_sendmsg+0xc14/0xe68
[   11.120968] [c0000001f803fa80] [c000000000700968] .sock_sendmsg+0xa0/0xe0
[   11.120975] [c0000001f803fbf0] [c0000000007014d8] .SyS_sendto+0x100/0x148
[   11.120983] [c0000001f803fd60] [c0000000006fff10] .SyS_socketcall+0x1c4/0x2e8
[   11.120990] [c0000001f803fe30] [c00000000000a1e4] syscall_exit+0x0/0x9c

Signed-off-by: Li Zhong <[email-masked]>
---
 net/packet/af_packet.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 9d70f13..20f6d56 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -237,6 +237,13 @@ struct packet_skb_cb {
 static void __fanout_unlink(struct sock *sk, struct packet_sock *po);
 static void __fanout_link(struct sock *sk, struct packet_sock *po);
 
+static u16 packet_pick_tx_queue(struct net_device *dev, struct sk_buff *skb)
+{
+	u16 queue_index = (u16)raw_smp_processor_id() % dev->real_num_tx_queues;
+	skb_set_queue_mapping(skb, queue_index);
+	return queue_index;
+}
+
 static int packet_direct_xmit(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
@@ -259,7 +266,7 @@ static int packet_direct_xmit(struct sk_buff *skb)
 		return NET_XMIT_DROP;
 	}
 
-	queue_map = skb_get_queue_mapping(skb);
+	queue_map = packet_pick_tx_queue(dev, skb);
 	txq = netdev_get_tx_queue(dev, queue_map);
 
 	__netif_tx_lock_bh(txq);
@@ -308,11 +315,6 @@ static bool packet_use_direct_xmit(const struct packet_sock *po)
 	return po->xmit == packet_direct_xmit;
 }
 
-static u16 packet_pick_tx_queue(struct net_device *dev)
-{
-	return (u16) smp_processor_id() % dev->real_num_tx_queues;
-}
-
 /* register_prot_hook must be invoked with the po->bind_lock held,
  * or from a context in which asynchronous accesses to the packet
  * socket is not possible (packet_create()).
@@ -2219,7 +2221,6 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 			}
 		}
 
-		skb_set_queue_mapping(skb, packet_pick_tx_queue(dev));
 		skb->destructor = tpacket_destruct_skb;
 		__packet_set_status(po, ph, TP_STATUS_SENDING);
 		atomic_inc(&po->tx_ring.pending);
@@ -2429,7 +2430,6 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	skb->dev = dev;
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
-	skb_set_queue_mapping(skb, packet_pick_tx_queue(dev));
 
 	if (po->has_vnet_hdr) {
 		if (vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {