Hey NBD Experts,
I ran into below kernel crash while testing NBD client/server failover.
Here is the stack dump I see on my Ubuntu-16.04 box.
[10554.029187] nbd: registered device at major 43
[10573.523556] EXT4-fs (nbd0): mounting ext2 file system using the ext4
subsystem
[10573.524366] EXT4-fs (nbd0): warning: mounting unchecked fs, running
e2fsck is recommended
[10573.524500] EXT4-fs (nbd0): mounted filesystem without journal. Opts:
(null)
[10591.278962] block nbd0: Receive control failed (result -512)
[10591.278971] block nbd0: pid 115995, nbd-client, got signal 9
[10591.278974] block nbd0: shutting down socket
[10638.646904] block nbd0: Attempted send on closed socket
[10638.646908] blk_update_request: I/O error, dev nbd0, sector 4632
[10638.646912] EXT4-fs warning (device nbd0): htree_dirblock_to_tree:958:
inode #2: lblock 0: comm ls: error -5 reading directory block
[10662.102399] ------------[ cut here ]------------
[10662.102420] kernel BUG at /build/linux-0XAgc4/linux-4.4.
0/fs/buffer.c:3005!
[10662.102427] invalid opcode: 0000 [#1] SMP
[10662.102434] Modules linked in: nbd ipt_MASQUERADE nf_nat_masquerade_ipv4
nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo iptable_nat
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype iptable_filter
ip_tables xt_conntrack x_tables nf_nat nf_conntrack br_netfilter bridge stp
llc aufs snd_hda_codec_hdmi binfmt_misc hp_wmi snd_hda_codec_realtek
sparse_keymap snd_hda_codec_generic input_leds intel_rapl
x86_pkg_temp_thermal intel_powerclamp snd_hda_intel coretemp snd_hda_codec
kvm_intel snd_hda_core snd_hwdep kvm snd_pcm irqbypass snd_seq_midi
snd_seq_midi_event snd_rawmidi snd_seq serio_raw snd_seq_device snd_timer
sb_edac edac_core lpc_ich snd mei_me mei soundcore shpchp tpm_infineon
8250_fintek mac_hid ib_iser rdma_cm iw_cm ib_cm ib_sa ib_mad ib_core
ib_addr iscsi_tcp libiscsi_tcp libiscsi
[10662.102572] scsi_transport_iscsi parport_pc ppdev lp parport autofs4
btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor
async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear hid_generic
usbhid hid nouveau crct10dif_pclmul crc32_pclmul ghash_clmulni_intel
aesni_intel aes_x86_64 mxm_wmi lrw video gf128mul glue_helper ablk_helper
i2c_algo_bit cryptd ttm drm_kms_helper syscopyarea sysfillrect e1000e
sysimgblt psmouse fb_sys_fops ptp ahci drm pps_core libahci wmi fjes [last
unloaded: nbd]
[10662.102673] CPU: 7 PID: 188844 Comm: umount Not tainted 4.4.0-78-generic
#99-Ubuntu
[10662.102679] Hardware name: Hewlett-Packard HP Z440 Workstation/212B,
BIOS M60 v02.31 12/14/2016
[10662.102686] task: ffff8807deb47000 ti: ffff8807d9e00000 task.ti:
ffff8807d9e00000
[10662.102692] RIP: 0010:[<ffffffff81247a62>] [<ffffffff81247a62>]
submit_bh_wbc+0x152/0x160
[10662.102706] RSP: 0018:ffff8807d9e03d40 EFLAGS: 00010246
[10662.102711] RAX: 0000000000000005 RBX: ffff88079bffbd00 RCX:
0000000000000000
[10662.102719] RDX: 0000000000000000 RSI: ffff88079bffbd00 RDI:
0000000000001411
[10662.103016] RBP: ffff8807d9e03d68 R08: 0000000000000000 R09:
0000000000000fff
[10662.103755] R10: 0000000000002d7c R11: 000000000000ef31 R12:
0000000000001411
[10662.104491] R13: 0000000000000008 R14: ffff8800c973a400 R15:
ffff880802f83800
[10662.105227] FS: 00007f538a5ba840(0000) GS:ffff88080c7c0000(0000)
knlGS:0000000000000000
[10662.105959] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[10662.106697] CR2: 0000000001a34878 CR3: 00000007deb1b000 CR4:
00000000001406e0
[10662.107431] Stack:
[10662.108161] ffff88079bffbd00 0000000000001411 0000000000000008
ffff8800c973a400
[10662.108902] ffff880802f83800 ffff8807d9e03d88 ffffffff812497bc
ffffffff81f38d80
[10662.109639] ffff88079bffbd00 ffff8807d9e03dd0 ffffffff812bbf42
0000000000000034
[10662.110378] Call Trace:
[10662.111100] [<ffffffff812497bc>] __sync_dirty_buffer+0x6c/0x100
[10662.111825] [<ffffffff812bbf42>] ext4_commit_super+0x1d2/0x290
[10662.112553] [<ffffffff812bccb1>] ext4_put_super+0xe1/0x390
[10662.113276] [<ffffffff812111ef>] generic_shutdown_super+0x6f/0x100
[10662.113988] [<ffffffff8121157c>] kill_block_super+0x2c/0xa0
[10662.114694] [<ffffffff812116d3>] deactivate_locked_super+0x43/0x70
[10662.115399] [<ffffffff81211bac>] deactivate_super+0x5c/0x60
[10662.116095] [<ffffffff8122fc0f>] cleanup_mnt+0x3f/0x90
[10662.116777] [<ffffffff8122fca2>] __cleanup_mnt+0x12/0x20
[10662.117458] [<ffffffff8109f011>] task_work_run+0x81/0xa0
[10662.118138] [<ffffffff81003242>] exit_to_usermode_loop+0xc2/0xd0
[10662.118805] [<ffffffff81003c6e>] syscall_return_slowpath+0x4e/0x60
[10662.119469] [<ffffffff81840b90>] int_ret_from_sys_call+0x25/0x8f
[10662.120121] Code: 44 89 ef e8 81 14 18 00 5b 31 c0 41 5c 41 5d 41 5e 41
5f 5d c3 40 f6 c7 01 0f 84 1c ff ff ff f0 80 63 01 f7 e9 12 ff ff ff 0f 0b
<0f> 0b 0f 0b 0f 0b 0f 0b 0f 0b 0f 1f 40 00 0f 1f 44 00 00 55 31
[10662.121487] RIP [<ffffffff81247a62>] submit_bh_wbc+0x152/0x160
[10662.122161] RSP <ffff8807d9e03d40>
I have both nbd-server and nbd-client running on the same system, and issue
can be reproduced with following commands,
**Server
truncate -s 10G /mnt/nbddisk
mkfs.ext4 /mnt/nbddisk
nbd-server 127.0.0.1@9000 /mnt/nbddisk
**Client
modprobe nbd
nbd-client 127.0.0.1 9000 /dev/nbd0
mount /dev/nbd0 /mnt/
kill -9 <pid of nbd-client>
After killing nbd-client, remounting /dev/nbd0 to different folder fails
with "/dev/nbd0 is already mounted or /mnt1/" busy".
Unmounting "/mnt" leads to above kernel crash.
I found below thread reporting the similar crash. I see thread concluded
with suggestions, but not sure if the fix is pushed to the mainstream
kernel or not.
https://sourceforge.net/p/nbd/mailman/message/34486113/
Is there any way this can be fixed in the driver? I would be glad to help
in verifying the fix if needed.
Thanks,
Mehul.
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