[bug report v4.8] fs/locks.c: kernel oops during posix lock stress test

[Ming Lei]

Hi Guys,

When I run stress-ng via the following steps on one ARM64 dual
socket system(Cavium Thunder), the kernel oops[1] can often be
triggered after running the stress test for several hours(sometimes
it may take longer):

- git clone git://kernel.ubuntu.com/cking/stress-ng.git
- apply the attachment patch which just makes the posix file
lock stress test more aggressive
- run the test via '~/git/stress-ng$./stress-ng --lockf 128 --aggressive'


>From the oops log, looks one garbage file_lock node is got
from the linked list of 'ctx->flc_posix' when the issue happens.

BTW, the issue isn't observed on single socket Cavium Thunder yet,
and the same issue can be seen on Ubuntu Xenial(v4.4 based kernel)
too.

Thanks,
Ming

[1] kernel oops log
ubuntu at ubuntu:~/git/stress-ng$ ./stress-ng --lockf 128 --aggressive
stress-ng: info:  [63828] defaulting to a 86400 second run per stressor
stress-ng: info:  [63828] dispatching hogs: 128 lockf
stress-ng: info:  [63828] cache allocate: default cache size: 16384K
[80659.799092] Unable to handle kernel NULL pointer dereference at
virtual address 00000030
[80659.807219] pgd = ffff81001f365800
[80659.810683] [00000030] *pgd=000001001a290003,
*pud=000001001a290003, *pmd=0000010fa07f0003, *pte=0000000000000000
[80659.821029] Internal error: Oops: 96000007 [#1] SMP
[80659.825901] Modules linked in:
[80659.828962] CPU: 15 PID: 63848 Comm: stress-ng-lockf Tainted: G
   W       4.8.0 #167
[80659.837132] Hardware name: Cavium ThunderX CRB/To be filled by
O.E.M., BIOS 5.11 12/12/2012
[80659.845479] task: ffff81001ee78580 task.stack: ffff81001f798000
[80659.851402] PC is at posix_locks_conflict+0x94/0xc0
[80659.856282] LR is at posix_lock_inode+0x90/0x6b0
[80659.860896] pc : [<ffff00000828c694>] lr : [<ffff00000828cd90>]
pstate: a0000145
[80659.868285] sp : ffff81001f79bca0
[80659.871596] x29: ffff81001f79bca0 x28: ffff81001f798000
[80659.876915] x27: ffff800fdffbc160 x26: 0000000000000000
[80659.882234] x25: ffff800fd2da2b30 x24: ffff800fce927430
[80659.887551] x23: ffff800fce92d8f0 x22: ffff81001f79bd30
[80659.892869] x21: ffff800fd2da2b18 x20: fffffffffffffff8
[80659.898187] x19: ffff800fdffbc160 x18: 0000000000001140
[80659.903504] x17: 0000ffff8870a578 x16: ffff000008245768
[80659.908821] x15: 0000ffff888bc000 x14: 0000000000000000
[80659.914139] x13: 00000003e8000000 x12: 0000000000000018
[80659.919457] x11: 00000000000e6a17 x10: 00000000ffffffd0
[80659.924776] x9 : 0000000000000000 x8 : ffff800fce927500
[80659.930094] x7 : 0000000000000000 x6 : 000000000000007f
[80659.935413] x5 : 0000000000000080 x4 : ffff800fce927438
[80659.940729] x3 : ffff800fce927458 x2 : 00000000000026b9
[80659.946047] x1 : ffff81001f37f300 x0 : 0000000000000000
[80659.951363]
[80659.952851] Process stress-ng-lockf (pid: 63848, stack limit =
0xffff81001f798020)
[80659.960415] Stack: (0xffff81001f79bca0 to 0xffff81001f79c000)
[80659.966158] bca0: ffff81001f79bcc0 ffff00000828cd90
fffffffffffffff8 ffff800fa3a66568
[80659.973986] bcc0: ffff81001f79bd40 ffff00000828d5f0
ffff800f8185c700 ffff800fdffbc160
[80659.981812] bce0: 0000000000000006 0000000000000000
ffff81001f79bdd0 0000000000000006
[80659.989638] bd00: 0000000000000120 0000000000000019
ffff0000088b1000 ffff81001f798000
[80659.997465] bd20: ffff81001f79bd40 ffff000008403fec
ffff81001f79bd30 ffff81001f79bd30
[80660.005292] bd40: ffff81001f79bd70 ffff00000828d8bc
ffff800f8185c700 ffff800fdffbc160
[80660.013118] bd60: ffff800fdffbc1b8 ffff800f8185c700
ffff81001f79bde0 ffff00000828ef10
[80660.020944] bd80: ffff800f8185c700 0000000000000000
ffff800fdffbc160 ffff800fa3a66568
[80660.028770] bda0: 0000000000000006 0000000000000004
ffff81001f79bde0 ffff00000828ee14
[80660.036596] bdc0: ffff800f8185c700 00000000fffffff2
ffff800fdffbc160 ffff810ff99aae80
[80660.044423] bde0: ffff81001f79be70 ffff000008245b84
ffff800f8185c700 ffff800f8185c700
[80660.052249] be00: 0000000000000000 0000000000000006
0000ffffdad5d4b0 0000000000000004
[80660.060087] be20: 0000000000000120 000000000000003e
0000000000010001 0000000000000000
[80660.067916] be40: 0000000000000008 0000000000000000
0000000000010001 0000000000000000
[80660.075742] be60: 0000000000000008 0000000000000000
0000000000000000 ffff0000080836f0
[80660.083568] be80: 0000000000000000 00000000005c5000
ffffffffffffffff 0000ffff8870a3b8
[80660.091394] bea0: 0000000080000000 0000000000000015
0000000080000000 00000000005c5000
[80660.099220] bec0: 0000000000000004 0000000000000006
0000ffffdad5d4b0 00000000ffffff80
[80660.107046] bee0: 0000ffffdad5d490 0000000026c26373
000000000000176f 0000000000004650
[80660.114873] bf00: 0000000000000019 0000000000006536
00000000ffffffd0 00000000000e6a17
[80660.122698] bf20: 0000000000000018 00000003e8000000
0000000000000000 0000ffff888bc000
[80660.130524] bf40: 000000000048a170 0000ffff8870a578
0000000000001140 000000000000055f
[80660.138351] bf60: 00000000005c5000 0000000000000004
0000ffff879f9008 0000000000000000
[80660.146177] bf80: 0000000000000002 000000000048b530
2001000800400201 0000ffffdad60758
[80660.154004] bfa0: 000000000048b008 0000ffffdad5d390
0000ffff8870a518 0000ffffdad5d390
[80660.161830] bfc0: 0000ffff8870a3b8 0000000080000000
0000000000000004 0000000000000019
[80660.169656] bfe0: 0000000000000000 0000000000000000
0000000000000000 0000000000000000
[80660.177481] Call trace:
[80660.179928] Exception stack(0xffff81001f79bad0 to 0xffff81001f79bc00)
[80660.186365] bac0:
ffff800fdffbc160 0001000000000000
[80660.194192] bae0: ffff81001f79bca0 ffff00000828c694
ffff800fc0002c00 ffff81001ee78600
[80660.202017] bb00: ffff81001f79bb70 ffff00000820b57c
ffff800fcb2a6d88 ffff800fc0002c00
[80660.209843] bb20: 0000000000000001 ffff810008ddbf00
ffff81001f79bc30 ffff81001f79bc30
[80660.217670] bb40: 0000000000000000 ffff810fa0712be8
ffff800f81dfd680 ffff810fa0712be8
[80660.225496] bb60: 0000000000000001 ffff810008ddbf00
0000000000000000 ffff81001f37f300
[80660.233322] bb80: 00000000000026b9 ffff800fce927458
ffff800fce927438 0000000000000080
[80660.241148] bba0: 000000000000007f 0000000000000000
ffff800fce927500 0000000000000000
[80660.248974] bbc0: 00000000ffffffd0 00000000000e6a17
0000000000000018 00000003e8000000
[80660.256800] bbe0: 0000000000000000 0000ffff888bc000
ffff000008245768 0000ffff8870a578
[80660.264636] [<ffff00000828c694>] posix_locks_conflict+0x94/0xc0
[80660.270559] [<ffff00000828cd90>] posix_lock_inode+0x90/0x6b0
[80660.276220] [<ffff00000828d5f0>] vfs_lock_file+0x68/0x78
[80660.281537] [<ffff00000828d8bc>] do_lock_file_wait+0x54/0xe0
[80660.287199] [<ffff00000828ef10>] fcntl_setlk+0x1c0/0x308
[80660.292513] [<ffff000008245b84>] SyS_fcntl+0x41c/0x5b8
[80660.297653] [<ffff0000080836f0>] el0_svc_naked+0x24/0x28
[80660.302961] Code: a8c27bfd d65f03c0 d503201f f9401e61 (f9401e80)
[80660.309188] ---[ end trace aa50050684d3a3fe ]---
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