Commit 8625b2f8 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Luis Henriques

ip_tunnel: disable preemption when updating per-cpu tstats

commit b4fe85f9 upstream.

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]  [<ffffffff8234e936>] dump_stack+0x4f/0x7b
[  188.435615]  [<ffffffff81915f3d>] check_preemption_disabled+0x19d/0x1c0
[  188.435619]  [<ffffffff81915f77>] 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: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Acked-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent d9850f8e
......@@ -79,11 +79,12 @@ static inline void ip6tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
err = ip6_local_out(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++;
......
......@@ -166,12 +166,13 @@ 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++;
......
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