From: Jason A. Donenfeld Date: Thu, 12 Nov 2015 16:35:58 +0000 (+0100) Subject: ip_tunnel: disable preemption when updating per-cpu tstats X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=b4fe85f9c9146f60457e9512fb6055e69e6a7a65;p=openwrt%2Fstaging%2Fblogic.git ip_tunnel: disable preemption when updating per-cpu tstats Drivers like vxlan use the recently introduced udp_tunnel_xmit_skb/udp_tunnel6_xmit_skb APIs. udp_tunnel6_xmit_skb makes use of ip6tunnel_xmit, and ip6tunnel_xmit, after sending the packet, updates the struct stats using the usual u64_stats_update_begin/end calls on this_cpu_ptr(dev->tstats). udp_tunnel_xmit_skb makes use of iptunnel_xmit, which doesn't touch tstats, so drivers like vxlan, immediately after, call iptunnel_xmit_stats, which does the same thing - calls u64_stats_update_begin/end on this_cpu_ptr(dev->tstats). While vxlan is probably fine (I don't know?), calling a similar function from, say, an unbound workqueue, on a fully preemptable kernel causes real issues: [ 188.434537] BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u8:0/6 [ 188.435579] caller is debug_smp_processor_id+0x17/0x20 [ 188.435583] CPU: 0 PID: 6 Comm: kworker/u8:0 Not tainted 4.2.6 #2 [ 188.435607] Call Trace: [ 188.435611] [] dump_stack+0x4f/0x7b [ 188.435615] [] check_preemption_disabled+0x19d/0x1c0 [ 188.435619] [] debug_smp_processor_id+0x17/0x20 The solution would be to protect the whole this_cpu_ptr(dev->tstats)/u64_stats_update_begin/end blocks with disabling preemption and then reenabling it. Signed-off-by: Jason A. Donenfeld Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h index aaee6fa02cf1..ff788b665277 100644 --- a/include/net/ip6_tunnel.h +++ b/include/net/ip6_tunnel.h @@ -90,11 +90,12 @@ static inline void ip6tunnel_xmit(struct sock *sk, struct sk_buff *skb, err = ip6_local_out(dev_net(skb_dst(skb)->dev), sk, skb); if (net_xmit_eval(err) == 0) { - struct pcpu_sw_netstats *tstats = this_cpu_ptr(dev->tstats); + struct pcpu_sw_netstats *tstats = get_cpu_ptr(dev->tstats); u64_stats_update_begin(&tstats->syncp); tstats->tx_bytes += pkt_len; tstats->tx_packets++; u64_stats_update_end(&tstats->syncp); + put_cpu_ptr(tstats); } else { stats->tx_errors++; stats->tx_aborted_errors++; diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h index f6dafec9102c..62a750a6a8f8 100644 --- a/include/net/ip_tunnels.h +++ b/include/net/ip_tunnels.h @@ -287,12 +287,13 @@ static inline void iptunnel_xmit_stats(int err, struct pcpu_sw_netstats __percpu *stats) { if (err > 0) { - struct pcpu_sw_netstats *tstats = this_cpu_ptr(stats); + struct pcpu_sw_netstats *tstats = get_cpu_ptr(stats); u64_stats_update_begin(&tstats->syncp); tstats->tx_bytes += err; tstats->tx_packets++; u64_stats_update_end(&tstats->syncp); + put_cpu_ptr(tstats); } else if (err < 0) { err_stats->tx_errors++; err_stats->tx_aborted_errors++;