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Subjectselftests: l2tp tests
Date
Hi,

While testing linux 5.4 with the l2tp test I discovered two kernel
issues when running this test:

1. About 10+ seconds after completing the test one can observe periodic
kernel log messages from netdev_wait_allrefs (in net/core/dev.c) in the
form:

"unregister_netdevice: waiting for eth0 to become free. Usage count = 1"

2. Our regression tests that ran stress-ng after this test picked up
another issue that causes socket() to hang indefinitely. I've managed
to get this down to a simple reproducer as follows:

sudo modprobe l2tp_core
sudo ./linux/tools/testing/selftests/net/l2tp.sh
sleep 5
./close

Where ./close is an executable compiled from:

#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>

int main()
{
int fd;

printf("calling socket..\n");
fd = socket(AF_APPLETALK, SOCK_STREAM, 0);
printf("socket returned: %d\n", fd);
}

The code will hang on the socket() call and won't ever get to the final
print statement.

If one runs the reproducer on earlier kernels we get:

4.6.7 crash (see dmesg below)
4.7.10 crash in xfrm6_dst_ifdown
4.8.17 crash in xfrm6_dst_ifdown
4.12.14 crash (see dmesg below)
4.13.16 reports "unregister_netdevice: waiting for eth0 to become free.
Usage count = 2"
4.14.157 reports "unregister_netdevice: waiting for eth0 to become free.
Usage count = 2""
4.15.18 .. 5.4 hangs on socket() call

Note: functionality for the l2tp test is not available for pre-4.6 kernels.

The crashes I get for older kernels are:

4.6.7:
[ 34.457967] BUG: scheduling while atomic: kworker/u8:0/6/0x00000200
[ 34.458021] Modules linked in: esp6 xfrm6_mode_transport drbg
ansi_cprng seqiv esp4 xfrm4_mode_transport xfrm_user xfrm_algo l2tp_ip6
l2tp_eth l2tp_ip l2tp_netlink veth l2tp_core ip6_udp_tunnel udp_tunnel
squashfs binfmt_misc dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua
ppdev kvm_intel kvm irqbypass joydev input_leds snd_hda_codec_generic
serio_raw snd_hda_intel snd_hda_codec parport_pc 8250_fintek parport
snd_hda_core qemu_fw_cfg snd_hwdep snd_pcm snd_timer mac_hid snd
soundcore sch_fq_codel virtio_rng ip_tables x_tables autofs4 btrfs
raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor
async_tx xor hid_generic usbhid hid raid6_pq libcrc32c raid1 raid0
multipath linear crct10dif_pclmul crc32_pclmul ghash_clmulni_intel qxl
ttm drm_kms_helper syscopyarea sysfillrect aesni_intel sysimgblt
[ 34.458086] fb_sys_fops aes_x86_64 lrw gf128mul glue_helper ablk_helper
cryptd i2c_piix4 drm psmouse pata_acpi floppy
[ 34.458100] CPU: 1 PID: 6 Comm: kworker/u8:0 Not tainted
4.6.7-040607-generic #201608160432
[ 34.458103] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.12.0-1 04/01/2014
[ 34.458131] Workqueue: netns cleanup_net
[ 34.458135] 0000000000000286 000000002fa171e7 ffff88007c8e7ab8
ffffffff813f7594
[ 34.458139] ffff88007fc96b80 7fffffffffffffff ffff88007c8e7ac8
ffffffff810a8f6b
[ 34.458143] ffff88007c8e7b18 ffffffff8184905b 00ff88007c8e7ae8
ffffffff8106463e
[ 34.458147] Call Trace:
[ 34.458161] [<ffffffff813f7594>] dump_stack+0x63/0x8f
[ 34.458166] [<ffffffff810a8f6b>] __schedule_bug+0x4b/0x60
[ 34.458185] [<ffffffff8184905b>] __schedule+0x5eb/0x7a0
[ 34.458191] [<ffffffff8106463e>] ? kvm_sched_clock_read+0x1e/0x30
[ 34.458195] [<ffffffff81849245>] schedule+0x35/0x80
[ 34.458203] [<ffffffff8184c402>] schedule_timeout+0x1b2/0x270
[ 34.458207] [<ffffffff81848d74>] ? __schedule+0x304/0x7a0
[ 34.458212] [<ffffffff81849ca3>] wait_for_completion+0xb3/0x140
[ 34.458217] [<ffffffff810aeed0>] ? wake_up_q+0x70/0x70
[ 34.458226] [<ffffffff810e7f68>] __wait_rcu_gp+0xc8/0xf0
[ 34.458231] [<ffffffff810e9fd8>] synchronize_sched.part.58+0x38/0x50
[ 34.458235] [<ffffffff810ec570>] ? call_rcu_bh+0x20/0x20
[ 34.458239] [<ffffffff810e7e80>] ?
trace_raw_output_rcu_utilization+0x60/0x60
[ 34.458244] [<ffffffff810ec643>] synchronize_sched+0x33/0x40
[ 34.458251] [<ffffffffc0510f71>] __l2tp_session_unhash+0xd1/0xe0
[l2tp_core]
[ 34.458256] [<ffffffffc051101e>] l2tp_tunnel_closeall+0x9e/0x140
[l2tp_core]
[ 34.458261] [<ffffffffc0511219>] l2tp_tunnel_delete+0x19/0x70 [l2tp_core]
[ 34.458265] [<ffffffffc05112bb>] l2tp_exit_net+0x4b/0x80 [l2tp_core]
[ 34.458269] [<ffffffff81732188>] ops_exit_list.isra.4+0x38/0x60
[ 34.458273] [<ffffffff817331e4>] cleanup_net+0x1c4/0x2a0
[ 34.458281] [<ffffffff8109ccfc>] process_one_work+0x1fc/0x490
[ 34.458285] [<ffffffff8109cfdb>] worker_thread+0x4b/0x500
[ 34.458290] [<ffffffff8109cf90>] ? process_one_work+0x490/0x490
[ 34.458293] [<ffffffff810a37c8>] kthread+0xd8/0xf0
[ 34.458298] [<ffffffff8184d522>] ret_from_fork+0x22/0x40
[ 34.458302] [<ffffffff810a36f0>] ? kthread_create_on_node+0x1b0/0x1b0
[ 34.514067] ------------[ cut here ]------------

4.12.14:
[ 20.760253] ------------[ cut here ]------------
[ 20.760256] kernel BUG at
/home/kernel/COD/linux/net/ipv6/xfrm6_policy.c:265!
[ 20.760299] invalid opcode: 0000 [#1] SMP
[ 20.760320] Modules linked in: appletalk psnap llc esp6
xfrm6_mode_transport esp4 xfrm4_mode_transport xfrm_user xfrm_algo
l2tp_ip6 l2tp_eth l2tp_ip l2tp_netlink veth l2tp_core ip6_udp_tunnel
udp_tunnel binfmt_misc dm_multipath scsi_dh_rdac scsi_dh_emc
scsi_dh_alua joydev ppdev snd_hda_codec_generic kvm_intel kvm irqbypass
snd_hda_intel snd_hda_codec snd_hda_core input_leds snd_hwdep serio_raw
snd_pcm snd_timer hid_generic snd soundcore parport_pc parport mac_hid
qemu_fw_cfg sch_fq_codel virtio_rng ip_tables x_tables autofs4 usbhid
hid btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq
async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear
crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcbc aesni_intel
aes_x86_64 crypto_simd qxl glue_helper ttm cryptd drm_kms_helper psmouse
[ 20.760677] syscopyarea sysfillrect virtio_blk sysimgblt fb_sys_fops
drm floppy virtio_net i2c_piix4 pata_acpi
[ 20.760731] CPU: 3 PID: 49 Comm: kworker/u8:1 Not tainted
4.12.14-041214-generic #201709200843
[ 20.760772] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.12.0-1 04/01/2014
[ 20.760814] Workqueue: netns cleanup_net
[ 20.760836] task: ffff8aa4bcbbad00 task.stack: ffff9dc5804c0000
[ 20.760867] RIP: 0010:xfrm6_dst_ifdown+0xa0/0xb0
[ 20.760890] RSP: 0018:ffff9dc5804c3be0 EFLAGS: 00010246
[ 20.760916] RAX: ffff8aa4b6e6a000 RBX: ffff8aa4bc1b3500 RCX:
0000000000000000
[ 20.760950] RDX: 0000000000000001 RSI: ffff8aa4b6f39000 RDI:
ffff8aa4bc1b3500
[ 20.760984] RBP: ffff9dc5804c3c08 R08: 0000000000000000 R09:
ffffffffb49fd7a0
[ 20.761017] R10: ffff9dc5804c3c70 R11: 0000000000000000 R12:
ffff8aa4b6f39000
[ 20.761050] R13: ffff8aa4b6f39000 R14: ffff8aa4bc1b3500 R15:
0000000000000000
[ 20.761085] FS: 0000000000000000(0000) GS:ffff8aa4bfd80000(0000)
knlGS:0000000000000000
[ 20.761123] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 20.761150] CR2: 00007fa5cd126718 CR3: 000000007c382000 CR4:
00000000001406e0
[ 20.761189] Call Trace:
[ 20.761207] dst_ifdown+0x26/0x80
[ 20.761226] dst_dev_event+0x5c/0x170
[ 20.761247] notifier_call_chain+0x4a/0x70
[ 20.761269] raw_notifier_call_chain+0x16/0x20
[ 20.761293] call_netdevice_notifiers_info+0x35/0x60
[ 20.761318] netdev_run_todo+0xcf/0x300
[ 20.761340] rtnl_unlock+0xe/0x10
[ 20.761359] default_device_exit_batch+0x153/0x180
[ 20.761385] ? do_wait_intr_irq+0x90/0x90
[ 20.761408] ops_exit_list.isra.6+0x52/0x60
[ 20.761430] cleanup_net+0x1ca/0x2b0
[ 20.761451] process_one_work+0x1e7/0x410
[ 20.761472] worker_thread+0x4a/0x410
[ 20.761492] kthread+0x125/0x140
[ 20.761511] ? process_one_work+0x410/0x410
[ 20.761532] ? kthread_create_on_node+0x70/0x70
[ 20.761556] ret_from_fork+0x25/0x30
[ 20.761575] Code: f0 00 00 00 75 05 e8 10 6f 00 00 4c 89 bb 58 01 00 00
f0 41 ff 04 24 48 8b 5b 10 48 83 7b 48 00 75 d4 f0 41 ff 0c 24 eb 8e f3
c3 <0f> 0b 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 55 b9 06 00 00
[ 20.761695] RIP: xfrm6_dst_ifdown+0xa0/0xb0 RSP: ffff9dc5804c3be0
[ 20.762104] ---[ end trace b22472ed4abae541 ]---

So all in all, the test is great for finding bugs. I thought I should
flag these issues up.

Regards,

Colin

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