From: "Jason A. Donenfeld" <ja...@zx2c4.com> Date: Thu, 12 Nov 2015 17:35:58 +0100
> 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: Jason A. Donenfeld <ja...@zx2c4.com> Applied and queued up for -stable, thanks Jason Arguably, ip6tunnel_xmit() is primarily a ->ndo_start_xmit() and therefore could assume that it only ran inside of a BH disabled code sequence. And as you noted, when this was turned into a general case helper function that guarantee was no longer necessarily there. So another fix could have been to do local_bh_disable() in the udp_tunnel6_xmit_skb() helper. Thanks again. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
