Hi all, While upgrading my kernel from 5.2 to 5.4.43, I noticed a very sharp increase in CPU usage - coming from BIRD, the routing daemon on my system. I ran a Netlink capture and saw that BIRD was attempting to insert routes twice into the kernel routing table. This was causing routes to be re-inserted rapidly, and explained the increase of CPU usage.
I'm running IPv4 and IPv6 full tables - about 789,360 v4 routes and 78,185 v6 routes. About 10,000 routes fail to be re-inserted and this number fluctuated over time as the routing table was updated. The routes themselves are sourced from BGP peerings with upstreams on the router. I tried downgrading BIRD itself several times before realising that it must be a kernel issue, so I performed a bisect, and found this patch to be the issue: [PATCH net-next v7 04/11] ipv4: Dump route exceptions if requested https://lore.kernel.org/netdev/8d3b68cd37fb5fddc470904cdd6793fcf480c6c1.1561131177.git.sbri...@redhat.com/ When I added some debug logging to BIRD, I could see that before the patch BIRD was not receiving any FIB exception routes, but after the patch, it was receiving many. I suspect this is unrelated to the bigger issue here - even if I patch BIRD to reject these routes, the problem still occurs and BIRD keeps trying to re-insert routes into the kernel routing table twice. - Joseph Extra information: Kernel version: Linux version 5.4.43 (nixbld@localhost) (gcc version 9.2.0 (GCC)) #1-NixOS SMP Wed May 27 15:46:53 UTC 2020 Most recent kernel version which did not have the bug: 5.2.0 BIRD version I tested this on: 2.0.7 (also tested on 2.0.2 and other older versions) ver_linux output: Linux bdr1 5.4.43 #1-NixOS SMP Wed May 27 15:46:53 UTC 2020 x86_64 GNU/Linux Util-linux 2.33.2 Mount 2.33.2 Module-init-tools 26 E2fsprogs 1.45.5 Linux C Library 2.30 Dynamic linker (ldd) 2.30 Procps 3.3.16 Net-tools 1.60 Kbd 2.0.4 Console-tools 2.0.4 Sh-utils 8.31 Udev 243 Modules Loaded agpgart ata_generic ata_piix atkbd autofs4 bochs_drm bridge br_netfilter button cdrom crc16 crc32c_generic crc_ccitt dm_mod drm drm_kms_helper drm_vram_helper dummy ehci_hcd evdev ext4 failover fb_sys_fops floppy gre hid hid_generic i2c_core i2c_piix4 i8042 input_leds intel_agp intel_gtt ip6_gre ip6table_filter ip6table_nat ip6table_raw ip6_tables ip6_tunnel iptable_filter iptable_nat iptable_raw ip_tables ipv6 jbd2 joydev led_class libata libcrc32c libps2 llc loop mac_hid macvlan mbcache mousedev net_failover nf_conntrack nf_conntrack_netlink nf_defrag_ipv4 nf_defrag_ipv6 nf_log_common nf_log_ipv4 nf_log_ipv6 nf_nat nfnetlink overlay pata_acpi psmouse qemu_fw_cfg rng_core rtc_cmos sch_fq_codel scsi_mod serio serio_raw sr_mod stp syscopyarea sysfillrect sysimgblt tap ttm tun tunnel6 uhci_hcd usb_common usbcore usbhid veth virtio virtio_balloon virtio_blk virtio_console virtio_net virtio_pci virtio_ring virtio_rng xfrm_algo xfrm_user x_tables xt_addrtype xt_conntrack xt_LOG xt_MASQUERADE xt_multiport xt_nat xt_pkttype xt_tcpudp
