4.4.21-rt31-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bige...@linutronix.de>

It looks like the this_cpu_ptr() access in icmp_sk() is protected with
local_bh_disable(). To avoid missing serialization in -RT I am adding
here a local lock. No crash has been observed, this is just precaution.

Cc: stable...@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
 net/ipv4/icmp.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 74314d95d0f8..ff2593269089 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -78,6 +78,7 @@
 #include <linux/string.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/slab.h>
+#include <linux/locallock.h>
 #include <net/snmp.h>
 #include <net/ip.h>
 #include <net/route.h>
@@ -205,6 +206,8 @@ static const struct icmp_control 
icmp_pointers[NR_ICMP_TYPES+1];
  *
  *     On SMP we have one ICMP socket per-cpu.
  */
+static DEFINE_LOCAL_IRQ_LOCK(icmp_sk_lock);
+
 static struct sock *icmp_sk(struct net *net)
 {
        return *this_cpu_ptr(net->ipv4.icmp_sk);
@@ -216,12 +219,14 @@ static inline struct sock *icmp_xmit_lock(struct net *net)
 
        local_bh_disable();
 
+       local_lock(icmp_sk_lock);
        sk = icmp_sk(net);
 
        if (unlikely(!spin_trylock(&sk->sk_lock.slock))) {
                /* This can happen if the output path signals a
                 * dst_link_failure() for an outgoing ICMP packet.
                 */
+               local_unlock(icmp_sk_lock);
                local_bh_enable();
                return NULL;
        }
@@ -231,6 +236,7 @@ static inline struct sock *icmp_xmit_lock(struct net *net)
 static inline void icmp_xmit_unlock(struct sock *sk)
 {
        spin_unlock_bh(&sk->sk_lock.slock);
+       local_unlock(icmp_sk_lock);
 }
 
 int sysctl_icmp_msgs_per_sec __read_mostly = 1000;
@@ -359,6 +365,7 @@ static void icmp_push_reply(struct icmp_bxm *icmp_param,
        struct sock *sk;
        struct sk_buff *skb;
 
+       local_lock(icmp_sk_lock);
        sk = icmp_sk(dev_net((*rt)->dst.dev));
        if (ip_append_data(sk, fl4, icmp_glue_bits, icmp_param,
                           icmp_param->data_len+icmp_param->head_len,
@@ -381,6 +388,7 @@ static void icmp_push_reply(struct icmp_bxm *icmp_param,
                skb->ip_summed = CHECKSUM_NONE;
                ip_push_pending_frames(sk, fl4);
        }
+       local_unlock(icmp_sk_lock);
 }
 
 /*
-- 
2.8.1


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