[PATCH net-next] fix rtnl notification in atomic context

[Alexei Starovoitov <ast@plumgrid.com>]

commit 991fb3f74c "dev: always advertise rx_flags changes via netlink"
introduced rtnl notification from __dev_set_promiscuity(),
which can be called in atomic context.

Steps to reproduce:
ip tuntap add dev tap1 mode tap
ifconfig tap1 up
tcpdump -nei tap1 &
ip tuntap del dev tap1 mode tap

[  271.627994] device tap1 left promiscuous mode
[  271.639897] BUG: sleeping function called from invalid context at mm/slub.c:940
[  271.664491] in_atomic(): 1, irqs_disabled(): 0, pid: 3394, name: ip
[  271.677525] INFO: lockdep is turned off.
[  271.690503] CPU: 0 PID: 3394 Comm: ip Tainted: G        W    3.12.0-rc3+ #73
[  271.703996] Hardware name: System manufacturer System Product Name/P8Z77 WS, BIOS 3007 07/26/2012
[  271.731254]  ffffffff81a58506 ffff8807f0d57a58 ffffffff817544e5 ffff88082fa0f428
[  271.760261]  ffff8808071f5f40 ffff8807f0d57a88 ffffffff8108bad1 ffffffff81110ff8
[  271.790683]  0000000000000010 00000000000000d0 00000000000000d0 ffff8807f0d57af8
[  271.822332] Call Trace:
[  271.838234]  [<ffffffff817544e5>] dump_stack+0x55/0x76
[  271.854446]  [<ffffffff8108bad1>] __might_sleep+0x181/0x240
[  271.870836]  [<ffffffff81110ff8>] ? rcu_irq_exit+0x68/0xb0
[  271.887076]  [<ffffffff811a80be>] kmem_cache_alloc_node+0x4e/0x2a0
[  271.903368]  [<ffffffff810b4ddc>] ? vprintk_emit+0x1dc/0x5a0
[  271.919716]  [<ffffffff81614d67>] ? __alloc_skb+0x57/0x2a0
[  271.936088]  [<ffffffff810b4de0>] ? vprintk_emit+0x1e0/0x5a0
[  271.952504]  [<ffffffff81614d67>] __alloc_skb+0x57/0x2a0
[  271.968902]  [<ffffffff8163a0b2>] rtmsg_ifinfo+0x52/0x100
[  271.985302]  [<ffffffff8162ac6d>] __dev_notify_flags+0xad/0xc0
[  272.001642]  [<ffffffff8162ad0c>] __dev_set_promiscuity+0x8c/0x1c0
[  272.017917]  [<ffffffff81731ea5>] ? packet_notifier+0x5/0x380
[  272.033961]  [<ffffffff8162b109>] dev_set_promiscuity+0x29/0x50
[  272.049855]  [<ffffffff8172e937>] packet_dev_mc+0x87/0xc0
[  272.065494]  [<ffffffff81732052>] packet_notifier+0x1b2/0x380
[  272.080915]  [<ffffffff81731ea5>] ? packet_notifier+0x5/0x380
[  272.096009]  [<ffffffff81761c66>] notifier_call_chain+0x66/0x150
[  272.110803]  [<ffffffff8108503e>] __raw_notifier_call_chain+0xe/0x10
[  272.125468]  [<ffffffff81085056>] raw_notifier_call_chain+0x16/0x20
[  272.139984]  [<ffffffff81620190>] call_netdevice_notifiers_info+0x40/0x70
[  272.154523]  [<ffffffff816201d6>] call_netdevice_notifiers+0x16/0x20
[  272.168552]  [<ffffffff816224c5>] rollback_registered_many+0x145/0x240
[  272.182263]  [<ffffffff81622641>] rollback_registered+0x31/0x40
[  272.195369]  [<ffffffff816229c8>] unregister_netdevice_queue+0x58/0x90
[  272.208230]  [<ffffffff81547ca0>] __tun_detach+0x140/0x340
[  272.220686]  [<ffffffff81547ed6>] tun_chr_close+0x36/0x60

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
 include/linux/rtnetlink.h |    4 +++-
 net/core/dev.c            |    2 +-
 net/core/rtnetlink.c      |   12 +++++++++---
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index f28544b..26f5edc 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -15,7 +15,9 @@ extern int rtnetlink_put_metrics(struct sk_buff *skb, u32 *metrics);
 extern int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst,
 			      u32 id, long expires, u32 error);
 
-extern void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change);
+void __rtmsg_ifinfo(int type, struct net_device *dev, unsigned change,
+		    gfp_t flags);
+void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change);
 
 /* RTNL is used as a global lock for all changes to network configuration  */
 extern void rtnl_lock(void);
diff --git a/net/core/dev.c b/net/core/dev.c
index 0918aad..59b90fe 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5257,7 +5257,7 @@ void __dev_notify_flags(struct net_device *dev, unsigned int old_flags,
 	unsigned int changes = dev->flags ^ old_flags;
 
 	if (gchanges)
-		rtmsg_ifinfo(RTM_NEWLINK, dev, gchanges);
+		__rtmsg_ifinfo(RTM_NEWLINK, dev, gchanges, GFP_ATOMIC);
 
 	if (changes & IFF_UP) {
 		if (dev->flags & IFF_UP)
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 4aedf03..5931af9 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1984,14 +1984,15 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
-void rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change)
+void __rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change,
+		    gfp_t flags)
 {
 	struct net *net = dev_net(dev);
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 	size_t if_info_size;
 
-	skb = nlmsg_new((if_info_size = if_nlmsg_size(dev, 0)), GFP_KERNEL);
+	skb = nlmsg_new((if_info_size = if_nlmsg_size(dev, 0)), flags);
 	if (skb == NULL)
 		goto errout;
 
@@ -2002,12 +2003,17 @@ void rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change)
 		kfree_skb(skb);
 		goto errout;
 	}
-	rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL, GFP_KERNEL);
+	rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL, flags);
 	return;
 errout:
 	if (err < 0)
 		rtnl_set_sk_err(net, RTNLGRP_LINK, err);
 }
+
+void rtmsg_ifinfo(int type, struct net_device *dev, unsigned int change)
+{
+	__rtmsg_ifinfo(type, dev, change, GFP_KERNEL);
+}
 EXPORT_SYMBOL(rtmsg_ifinfo);
 
 static int nlmsg_populate_fdb_fill(struct sk_buff *skb,
-- 
1.7.9.5