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Date: Tue, 21 Dec 2021 06:16:15 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: Ignat Korchagin <ignat@...udflare.com>
Cc: netdev <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
David Ahern <dsahern@...nel.org>,
Jakub Kicinski <kuba@...nel.org>,
kernel-team <kernel-team@...udflare.com>
Subject: Re: tcp: kernel BUG at net/core/skbuff.c:3574!
On Tue, Dec 21, 2021 at 4:19 AM Ignat Korchagin <ignat@...udflare.com> wrote:
>
> Hi netdev,
>
> While trying to reproduce a different rare bug we're seeing in
> production I've triggered below on 5.15.9 kernel and confirmed on the
> latest netdev master tree:
>
Nothing comes to mind. skb_shift() has not been recently changed.
Why are you disabling TSO exactly ?
Is GRO being used on veth needed to trigger the bug ?
(GRO was added recently to veth, I confess I did not review the patches)
I guess you could replace the BUG_ON() to provide more details about
skb geometry.
> [ 53.970529][ C1] kernel BUG at net/core/skbuff.c:3574!
> [ 53.981755][ C1] invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> [ 53.982634][ C1] CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted
> 5.16.0-rc5+ #25
> [ 53.982634][ C1] Hardware name: QEMU Standard PC (Q35 + ICH9,
> 2009), BIOS 0.0.0 02/06/2015
> [ 53.982634][ C1] RIP: 0010:skb_shift+0x13ef/0x23b0
> [ 53.982634][ C1] Code: ea 03 0f b6 04 02 48 89 fa 83 e2 07 38 d0
> 7f 08 84 c0 0f 85 41 0c 00 00 41 80 7f 02 00 4d 8d b5 d0 00 00 00 0f
> 85 74 f5 ff ff <0f> 0b 4d 8d 77 20 be 04 00 00 00 4c 89 44 24 78 4c 89
> f7 4c 89 8c
> [ 53.982634][ C1] RSP: 0018:ffff8881008f7008 EFLAGS: 00010246
> [ 53.982634][ C1] RAX: 0000000000000000 RBX: ffff8881180b4c80
> RCX: 0000000000000000
> [ 53.982634][ C1] RDX: 0000000000000002 RSI: ffff8881180b4d3c
> RDI: ffff88810bc9cac2
> [ 53.982634][ C1] RBP: ffff8881008f70b8 R08: ffff8881180b4cf4
> R09: ffff8881180b4cf0
> [ 53.982634][ C1] R10: ffffed1022999e5c R11: 0000000000000002
> R12: 0000000000000590
> [ 53.982634][ C1] R13: ffff88810f940c80 R14: ffff88810f940d50
> R15: ffff88810bc9cac0
> [ 53.982634][ C1] FS: 0000000000000000(0000)
> GS:ffff888235880000(0000) knlGS:0000000000000000
> [ 53.982634][ C1] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 53.982634][ C1] CR2: 00007ff5f9b86680 CR3: 0000000108ce8004
> CR4: 0000000000170ee0
> [ 53.982634][ C1] Call Trace:
> [ 53.982634][ C1] <TASK>
> [ 53.982634][ C1] tcp_sacktag_walk+0xaba/0x18e0
> [ 53.982634][ C1] ? kasan_set_free_info+0x20/0x30
> [ 53.982634][ C1] ? __kasan_slab_free+0x10b/0x140
> [ 53.982634][ C1] ? slab_free_freelist_hook+0xb9/0x1d0
> [ 53.982634][ C1] ? kmem_cache_free+0x12f/0x350
> [ 53.982634][ C1] tcp_sacktag_write_queue+0xe7b/0x3460
> [ 53.982634][ C1] ? kasan_quarantine_put+0x87/0x1e0
> [ 53.982634][ C1] ? tcp_sacktag_walk+0x18e0/0x18e0
> [ 53.982634][ C1] ? slab_free_freelist_hook+0xb9/0x1d0
> [ 53.982634][ C1] ? sk_reset_timer+0x15/0x70
> [ 53.982634][ C1] ? kasan_quarantine_put+0x87/0x1e0
> [ 53.982634][ C1] tcp_ack+0x2666/0x54b0
> [ 53.982634][ C1] ? trace_hardirqs_on+0x1c/0x130
> [ 53.982634][ C1] ? asm_sysvec_apic_timer_interrupt+0x12/0x20
> [ 53.982634][ C1] ? tcp_fastretrans_alert+0x3260/0x3260
> [ 53.982634][ C1] ? tcp_validate_incoming+0x128/0x1c40
> [ 53.982634][ C1] ? tcp_reset+0x340/0x340
> [ 53.982634][ C1] ? rcu_read_lock_sched_held+0xc/0x70
> [ 53.982634][ C1] ? ktime_get+0x13c/0x160
> [ 53.982634][ C1] ? trace_hardirqs_on+0x1c/0x130
> [ 53.982634][ C1] ? ktime_get+0x9c/0x160
> [ 53.982634][ C1] tcp_rcv_established+0x4d9/0x20f0
> [ 53.982634][ C1] ? lock_release+0x700/0x700
> [ 53.982634][ C1] ? tcp_data_queue+0x5160/0x5160
> [ 53.982634][ C1] ? do_raw_spin_lock+0x12b/0x270
> [ 53.982634][ C1] ? rwlock_bug.part.0+0x90/0x90
> [ 53.982634][ C1] tcp_v4_do_rcv+0x551/0x810
> [ 53.982634][ C1] tcp_v4_rcv+0x22ed/0x2ed0
> [ 53.982634][ C1] ? lock_acquire+0x42a/0x4e0
> [ 53.982634][ C1] ? tcp_v4_early_demux+0x8d0/0x8d0
> [ 53.982634][ C1] ? lock_release+0x700/0x700
> [ 53.982634][ C1] ? inet_del_offload+0x50/0x50
> [ 53.982634][ C1] ? ip_local_deliver_finish+0x1e9/0x2f0
> [ 53.982634][ C1] ? lock_downgrade+0x6d0/0x6d0
> [ 53.982634][ C1] ip_protocol_deliver_rcu+0x96/0xaf0
> [ 53.982634][ C1] ip_local_deliver_finish+0x1e0/0x2f0
> [ 53.982634][ C1] ip_sublist_rcv_finish+0x211/0x440
> [ 53.982634][ C1] ip_list_rcv_finish.constprop.0+0x424/0x660
> [ 53.982634][ C1] ? ip_sublist_rcv_finish+0x440/0x440
> [ 53.982634][ C1] ? ip_rcv_core+0x5f6/0xc10
> [ 53.982634][ C1] ip_list_rcv+0x2c8/0x410
> [ 53.982634][ C1] ? ip_rcv+0x480/0x480
> [ 53.982634][ C1] ? ip_rcv+0x480/0x480
> [ 53.982634][ C1] __netif_receive_skb_list_core+0x65c/0x910
> [ 53.982634][ C1] ? process_backlog+0x710/0x710
> [ 53.982634][ C1] ? rcu_read_lock_sched_held+0xc/0x70
> [ 53.982634][ C1] ? rcu_read_lock_sched_held+0xc/0x70
> [ 53.982634][ C1] netif_receive_skb_list_internal+0x5f9/0xcb0
> [ 53.982634][ C1] ? __netif_receive_skb_list_core+0x910/0x910
> [ 53.982634][ C1] ? dev_gro_receive+0x700/0x2960
> [ 53.982634][ C1] ? do_raw_spin_lock+0x12b/0x270
> [ 53.982634][ C1] napi_complete_done+0x188/0x6e0
> [ 53.982634][ C1] gro_cell_poll+0x10c/0x1d0
> [ 53.982634][ C1] ? lock_downgrade+0x6d0/0x6d0
> [ 53.982634][ C1] __napi_poll+0xa1/0x530
> [ 53.982634][ C1] net_rx_action+0x567/0x1270
> [ 53.982634][ C1] ? napi_threaded_poll+0x470/0x470
> [ 53.982634][ C1] ? try_to_wake_up+0x101/0x1500
> [ 53.982634][ C1] ? migrate_swap_stop+0x7f0/0x7f0
> [ 53.982634][ C1] __do_softirq+0x28a/0x9ba
> [ 53.982634][ C1] ? do_softirq.part.0+0x110/0x110
> [ 53.982634][ C1] ? smpboot_thread_fn+0x6b/0x8c0
> [ 53.982634][ C1] run_ksoftirqd+0x32/0x60
> [ 53.982634][ C1] smpboot_thread_fn+0x559/0x8c0
> [ 53.982634][ C1] ? smpboot_register_percpu_thread+0x350/0x350
> [ 53.982634][ C1] kthread+0x3b9/0x490
> [ 53.982634][ C1] ? _raw_spin_unlock_irq+0x24/0x50
> [ 53.982634][ C1] ? set_kthread_struct+0x100/0x100
> [ 53.982634][ C1] ret_from_fork+0x22/0x30
> [ 53.982634][ C1] </TASK>
> [ 53.982634][ C1] Modules linked in:
> [ 54.939907][ C1] ---[ end trace f6c264574763a26f ]---
> [ 64.620726][ C1] RIP: 0010:skb_shift+0x13ef/0x23b0
> [ 64.630955][ C1] Code: ea 03 0f b6 04 02 48 89 fa 83 e2 07 38 d0
> 7f 08 84 c0 0f 85 41 0c 00 00 41 80 7f 02 00 4d 8d b5 d0 00 00 00 0f
> 85 74 f5 ff ff <0f> 0b 4d 8d 77 20 be 04 00 00 00 4c 89 44 24 78 4c 89
> f7 4c 89 8c
> [ 64.664945][ C1] RSP: 0018:ffff8881008f7008 EFLAGS: 00010246
> [ 64.675965][ C1] RAX: 0000000000000000 RBX: ffff8881180b4c80
> RCX: 0000000000000000
> [ 64.689670][ C1] RDX: 0000000000000002 RSI: ffff8881180b4d3c
> RDI: ffff88810bc9cac2
> [ 64.703383][ C1] RBP: ffff8881008f70b8 R08: ffff8881180b4cf4
> R09: ffff8881180b4cf0
> [ 64.717729][ C1] R10: ffffed1022999e5c R11: 0000000000000002
> R12: 0000000000000590
> [ 64.731377][ C1] R13: ffff88810f940c80 R14: ffff88810f940d50
> R15: ffff88810bc9cac0
> [ 64.744691][ C1] FS: 0000000000000000(0000)
> GS:ffff888235880000(0000) knlGS:0000000000000000
> [ 64.761003][ C1] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 64.773726][ C1] CR2: 00007ff5f9b86680 CR3: 0000000108ce8005
> CR4: 0000000000170ee0
> [ 64.789673][ C1] Kernel panic - not syncing: Fatal exception in interrupt
> [ 64.794751][ C1] Kernel Offset: 0x26000000 from
> 0xffffffff81000000 (relocation range:
> 0xffffffff80000000-0xffffffffbfffffff)
> [ 64.794751][ C1] ---[ end Kernel panic - not syncing: Fatal
> exception in interrupt ]---
>
> We are somehow triggering the BUG_ON directive in skbuff.c. Here is a
> bash script which triggers this in QEMU (may need to run it couple of
> times in a row):
>
> #!/bin/bash -xe
>
> ip netns delete left 2>/dev/null || true
> ip netns delete right 2>/dev/null || true
>
> ip netns add left
> ip netns add right
>
> ip link add veth-left netns left type veth peer veth-right netns right
>
> ip -n left link set lo up
> ip -n left link set veth-left up
>
> ip -n right link set lo up
> ip -n right link set veth-right up
>
> ip -n left addr add 192.168.13.5/24 dev veth-left
> ip -n right addr add 192.168.13.7/24 dev veth-right
>
> ip -n left tunnel add gre-left mode gre remote 192.168.13.7 local
> 192.168.13.5 ttl 255
> ip -n left link set gre-left up
> ip -n left addr add 10.10.10.5/24 dev gre-left
>
> ip -n right tunnel add gre-right mode gre remote 192.168.13.5 local
> 192.168.13.7 ttl 255
> ip -n right link set gre-right up
> ip -n right addr add 10.10.10.7/24 dev gre-right
>
> ip netns exec left ethtool -K veth-left gro on tso off
> ip netns exec right ethtool -K veth-right gro on tso off
>
> (ip netns exec right iperf3 -s -D && ip netns exec left iperf3 -c
> 10.10.10.7 -P 16 -b 100M) &
>
> sleep 5
>
> ip netns delete left
> ip netns delete right
>
> # end of script
>
> QEMU command line:
> qemu-system-x86_64 -nographic -cpu host \
> -enable-kvm \
> -machine q35 \
> -smp 8 \
> -m 8G \
> -drive
> if=pflash,format=raw,readonly=on,file=/usr/share/OVMF/OVMF_CODE.fd \
> -drive
> if=pflash,format=raw,file=/usr/share/OVMF/OVMF_VARS.fd \
> -drive file=/work/rootfs.img,format=qcow2 \
> -nic user,model=virtio-net-pci,hostfwd=tcp::22-:22 \
> -kernel vmlinuz \
> -append "console=ttyS0 root=/dev/sda rw
> systemd.unified_cgroup_hierarchy=0"
>
> Userspace: vanilla Debian Bullseye
>
> I didn't look deeply into it myself yet, but I think I don't even have
> enough knowledge about this code yet, so asking here for help.
>
> Thanks,
> Ignat
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