kernel BUG at drivers/net/phy/mdio_bus.c:451!

[Itaru Kitayama]

Hi,
Upon invocation of modprobe -r mdio_thunder on our ThunderX platform 
(v4.13 backed),
I observed a kernel BUG.

# modprobe -r mdio_thunder
[31764.217839] ------------[ cut here ]------------
[31764.226645] kernel BUG at drivers/net/phy/mdio_bus.c:451!
[31764.236205] Internal error: Oops - BUG: 0 [#1] SMP
[31764.245120] Modules linked in: nicpf thunder_bgx thunder_xcv 
xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 
iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 
xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc 
ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter vfat 
fat nicvf mdio_thunder(-) mdio_cavium sg ipmi_ssif aes_ce_blk 
crypto_simd cryptd ipmi_msghandler aes_ce_cipher ghash_ce 
uio_pdrv_genirq sha2_ce sha1_ce uio nfsd ip_tables xfs libcrc32c ast 
i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt 
fb_sys_fops ttm drm i2c_core dm_mirror dm_region_hash dm_log dm_mod dax 
[last unloaded: thunder_xcv]
[31764.323084] CPU: 52 PID: 6959 Comm: modprobe Tainted: G W       
4.13.0-dev #3
[31764.335511] Hardware name: GIGABYTE R150-T62-00/MT60-SC3-00, BIOS T43 
05/18/2017
[31764.347587] task: ffffff07f029ff80 task.stack: ffffff07d9154000
[31764.358177] PC is at mdiobus_free+0x54/0x58
[31764.366993] LR is at _devm_mdiobus_free+0x20/0x28
[31764.376291] pc : [<fffffc00085cc618>] lr : [<fffffc00085cc63c>] 
pstate: 20000145
[31764.388308] sp : ffffff07d9157c80
[31764.396183] x29: ffffff07d9157c80 x28: 0000000000000000
[31764.406036] x27: fffffc0008552664 x26: ffffff07f91a5330
[31764.415860] x25: fffffc000855267c x24: 0000000000000005
[31764.425633] x23: ffffff07f91a50a0 x22: ffffff07d9157d30
[31764.435364] x21: ffffff07f91a5330 x20: ffffff0016989900
[31764.445070] x19: ffffff07f4f30800 x18: 000003ffde5b6bb0
[31764.454745] x17: 0000000000000000 x16: ffffff07f029ff80
[31764.464380] x15: 0000000000005788 x14: 0000000000000000
[31764.473960] x13: 0000000000000040 x12: 0000000000000220
[31764.483515] x11: 0000000000000000 x10: 0000000000000000
[31764.493013] x9 : ffffff07d901e000 x8 : ffffff000141fc00
[31764.502485] x7 : fffffdffc005a600 x6 : 000000000000240e
[31764.511911] x5 : ffffff0016989900 x4 : ffffff0016989900
[31764.521287] x3 : ffffff07d9157d30 x2 : fffffc00085cc61c
[31764.530627] x1 : ffffff0016989d18 x0 : 0000000000000004
[31764.539917] Process modprobe (pid: 6959, stack limit = 
0xffffff07d9154000)
[31764.550777] Stack: (0xffffff07d9157c80 to 0xffffff07d9158000)
[31764.560501] 7c80: ffffff07d9157ca0 fffffc00085cc63c ffffff0016989d00 
fffffc0008553770
[31764.572335] 7ca0: ffffff07d9157cc0 fffffc000855379c ffffff07d9157cc0 
ffffff0016989d18
[31764.584118] 7cc0: ffffff07d9157d40 fffffc00085539c0 ffffff07f91a50a0 
ffffff07f91a5100
[31764.595866] 7ce0: ffffff07f915d0a0 fffffc00039b0068 ffffff07f915d100 
0000000000000015
[31764.607576] 7d00: 0000000000000124 000000000000006a fffffc0008841000 
ffffff07f029ff80
[31764.619267] 7d20: ffffff0016989900 0000000000000140 ffffff0016987700 
ffffff0016989d00
[31764.630937] 7d40: ffffff07d9157d60 fffffc000854ed3c ffffff07f91a50a0 
ffffff07f91a5100
[31764.642575] 7d60: ffffff07d9157da0 fffffc000854ee28 ffffff07f91a50a0 
fffffc00039b0068
[31764.654154] 7d80: fffffc0008e3ab28 fffffc00039b0000 0000000080000000 
dead000000000100
[31764.665725] 7da0: ffffff07d9157dc0 fffffc000854da58 fffffc00039b0068 
fffffc0008e3a000
[31764.677270] 7dc0: ffffff07d9157df0 fffffc000854f7f8 fffffc00039b0068 
fffffc000946a000
[31764.688747] 7de0: fffffc0008d9f000 000003ff9ab4b9f8 ffffff07d9157e10 
fffffc000846539c
[31764.700210] 7e00: fffffc00039b0100 fffffc000946a000 ffffff07d9157e40 
fffffc0003990350
[31764.711635] 7e20: fffffc00039b0100 fffffc000946a000 fffffc0008d9f000 
000003ff9ab4b9f8
[31764.723010] 7e40: ffffff07d9157e50 fffffc000814d668 0000000000000000 
fffffc000808344c
[31764.734375] 7e60: 0000000000000200 00000307f19f0000 ffffffffffffffff 
0000000000418710
[31764.745733] 7e80: 0000000000000800 7568745f6f69646d 000000007265646e 
fffffc000808341c
[31764.757066] 7ea0: 0000000000000200 00000307f19f0000 ffffffffffffffff 
000003ff9ab3d738
[31764.768394] 7ec0: 0000000020e604d8 0000000000000800 0000000000418710 
0000000000002002
[31764.779697] 7ee0: 000003ff9abf0e48 000003ffde5b5db9 000003ff9aab9c78 
000000000000001f
[31764.790964] 7f00: 000000000000006a 607c4a80bc7d3400 00000000ffffffff 
0000000000000000
[31764.802220] 7f20: 0000000000000005 ffffffffffffffff 0000000020e61699 
0000000000005788
[31764.813441] 7f40: 000003ff9ab4b9f0 0000000000440320 000003ffde5b6bb0 
0000000020e60470
[31764.824712] 7f60: 0000000020e604d8 0000000000000001 0000000000000000 
0000000020e604d8
[31764.836016] 7f80: 0000000020e60470 0000000020e60010 0000000000440000 
000003ffde5b8278
[31764.847281] 7fa0: 0000000000000000 000003ffde5b6de0 00000000004114f4 
000003ffde5b6de0
[31764.858528] 7fc0: 000003ff9ab4b9f8 0000000080000000 0000000020e604d8 
000000000000006a
[31764.869774] 7fe0: 0000000000000000 0000000000000000 0000000000000000 
0000000000000000
[31764.880873] Call trace:
[31764.886418] Exception stack(0xffffff07d9157ab0 to 0xffffff07d9157be0)
[31764.895881] 7aa0: ffffff07f4f30800 0000040000000000
[31764.906635] 7ac0: ffffff07d9157c80 fffffc00085cc618 ffffff07d9157bd0 
fffffc00082512c8
[31764.917303] 7ae0: ffffff0016989a00 ffffff0016989a00 fffffc0008547cec 
fffffc0008afdf40
[31764.927936] 7b00: ffffff000141f600 fffffc0009560ce0 ffffff07d9157c10 
fffffc00082512c8
[31764.938533] 7b20: ffffff000141fa80 ffffff07f4f30800 ffffff000141fc00 
fffffc00082512c8
[31764.949100] 7b40: ffffff07d9157c40 fffffc00082512c8 0000000000000004 
ffffff0016989d18
[31764.959680] 7b60: fffffc00085cc61c ffffff07d9157d30 ffffff0016989900 
ffffff0016989900
[31764.970233] 7b80: 000000000000240e fffffdffc005a600 ffffff000141fc00 
ffffff07d901e000
[31764.980763] 7ba0: 0000000000000000 0000000000000000 0000000000000220 
0000000000000040
[31764.991315] 7bc0: 0000000000000000 0000000000005788 ffffff07f029ff80 
0000000000000000
[31765.001861] [<fffffc00085cc618>] mdiobus_free+0x54/0x58
[31765.009824] [<fffffc00085cc63c>] _devm_mdiobus_free+0x20/0x28
[31765.018321] [<fffffc000855379c>] release_nodes+0x188/0x298
[31765.026567] [<fffffc00085539c0>] devres_release_all+0x3c/0x54
[31765.035081] [<fffffc000854ed3c>] 
device_release_driver_internal+0x164/0x1cc
[31765.044830] [<fffffc000854ee28>] driver_detach+0x50/0x94
[31765.052932] [<fffffc000854da58>] bus_remove_driver+0x74/0xe8
[31765.061410] [<fffffc000854f7f8>] driver_unregister+0x34/0x54
[31765.069911] [<fffffc000846539c>] pci_unregister_driver+0x24/0xbc
[31765.078771] [<fffffc0003990350>] 
thunder_mdiobus_driver_exit+0x10/0xfcc0 [mdio_thunder]
[31765.089693] [<fffffc000814d668>] SyS_delete_module+0x1b0/0x20c
[31765.098446] [<fffffc000808344c>] __sys_trace_return+0x0/0x4
[31765.106949] Code: d65f03c0 aa1303e0 97f212d3 17fffffb (d4210000)
[31765.116043] ---[ end trace 3849ffa22d300da4 ]---
[31765.123597] Kernel panic - not syncing: Fatal exception
[31765.131764] SMP: stopping secondary CPUs
[31765.138610] Kernel Offset: disabled
[31765.144972] CPU features: 0x101108
[31765.151246] Memory Limit: none
[31765.157173] ---[ end Kernel panic - not syncing: Fatal exception