FYI, we noticed the following commit:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
commit 8430e7e0af9a15063b90343e3beebc164c8e90f3 ("md: disconnect device from personality before trying to remove it.")

in testcase: mdadm-selftests
with following parameters:

	test_prefix: 10


on test machine: 8 threads Nehalem with 4G memory

caused below changes:


+--------------------------------------------------------------+------------+------------+
|                                                              | 7ac5044722 | 8430e7e0af |
+--------------------------------------------------------------+------------+------------+
| boot_successes                                               | 13         | 4          |
| boot_failures                                                | 0          | 11         |
| BUG:unable_to_handle_kernel                                  | 0          | 11         |
| Oops                                                         | 0          | 11         |
| RIP:remove_and_add_spares                                    | 0          | 10         |
| Kernel_panic-not_syncing:Fatal_exception                     | 0          | 10         |
| backtrace:vfs_write+0x                                       | 0          | 10         |
| backtrace:SyS_write+0x                                       | 0          | 10         |
| WARNING:at_arch/x86/kernel/smp.c:#native_smp_send_reschedule | 0          | 1          |
+--------------------------------------------------------------+------------+------------+



[   31.258520] md: bind<loop9>
[   31.258925] md: bind<loop8>
[   31.299842] md: bind<loop10>
[   31.303080] BUG: unable to handle kernel NULL pointer dereference at 0000000000000050
[   31.303611] IP: [<ffffffff817752f6>] remove_and_add_spares+0x236/0x310
[   31.303995] PGD 8422c067 PUD 92d3a067 PMD 0 
[   31.304363] Oops: 0000 [#1] SMP
[   31.304590] Modules linked in: multipath loop raid456 async_raid6_recov async_memcpy async_pq async_xor xor async_tx raid6_pq raid10 raid1 raid0 rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver netconsole sg sr_mod sd_mod cdrom dcdbas ata_generic snd_hda_codec_realtek pata_acpi snd_hda_codec_generic i7core_edac coretemp kvm_intel snd_hda_codec_hdmi kvm ata_piix irqbypass crc32c_intel pcspkr serio_raw edac_core usb_storage libata snd_hda_intel firewire_ohci firewire_core crc_itu_t snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_timer snd soundcore shpchp acpi_cpufreq broadcom bcm_phy_lib
[   31.308998] CPU: 0 PID: 876 Comm: mdadm Not tainted 4.6.0-10682-g8430e7e #1
[   31.309361] Hardware name: Dell Inc. Studio XPS 8000/0X231R, BIOS A01 08/11/2009
[   31.309882] task: ffff8800977da480 ti: ffff880084534000 task.ti: ffff880084534000
[   31.310327] RIP: 0010:[<ffffffff817752f6>]  [<ffffffff817752f6>] remove_and_add_spares+0x236/0x310
[   31.310863] RSP: 0018:ffff880084537d40  EFLAGS: 00010246
[   31.311163] RAX: 0000000000000000 RBX: ffff8800a2377600 RCX: 0000000000000000
[   31.311532] RDX: 0000000000000000 RSI: ffff8800a2377600 RDI: ffff8800a0d9c800
[   31.311901] RBP: ffff880084537d98 R08: 0000000000000000 R09: ffff8800a0d9c848
[   31.312270] R10: 00007f50ade33760 R11: 0000000000000246 R12: ffff8800a2377600
[   31.312640] R13: ffff8800a0d9c818 R14: ffff8800a0d9c800 R15: ffff8800a0d9c801
[   31.313009] FS:  00007f50ae254700(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000
[   31.313477] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   31.313793] CR2: 0000000000000050 CR3: 000000008455b000 CR4: 00000000000006f0
[   31.314162] Stack:
[   31.314335]  ffff8800a0d9c848 ffff880000000000 ffff8800a0d9c800 ffff880084537d68
[   31.314909]  ffffffff813cb570 ffff880084537d98 ffff8800a2377600 ffff880135d40000
[   31.315483]  0000000000000006 0000000000000006 ffff8800a0d9c800 ffff880084537dc0
[   31.316057] Call Trace:
[   31.316250]  [<ffffffff813cb570>] ? selinux_capable+0x20/0x30
[   31.316567]  [<ffffffff81779401>] state_store+0x81/0x410
[   31.316868]  [<ffffffff8176fda7>] rdev_attr_store+0x77/0xb0
[   31.317179]  [<ffffffff812813f7>] sysfs_kf_write+0x37/0x40
[   31.317485]  [<ffffffff81280754>] kernfs_fop_write+0x134/0x1c0
[   31.317807]  [<ffffffff811ff9f8>] __vfs_write+0x28/0x120
[   31.318109]  [<ffffffff810a3989>] ? __might_sleep+0x49/0x80
[   31.318420]  [<ffffffff810c8f35>] ? percpu_down_read+0x25/0x70
[   31.318740]  [<ffffffff81200b75>] vfs_write+0xb5/0x1a0
[   31.319034]  [<ffffffff81201eb6>] SyS_write+0x46/0xa0
[   31.321012]  [<ffffffff81919f72>] entry_SYSCALL_64_fastpath+0x1a/0xa4
[   31.321354] Code: 00 00 00 a8 04 0f 85 6a ff ff ff 48 c7 83 e8 00 00 00 00 00 00 00 49 8b 46 08 4c 89 4d a8 48 89 de 89 4d b0 44 88 45 b8 4c 89 f7 <ff> 50 50 85 c0 44 0f b6 45 b8 8b 4d b0 4c 8b 4d a8 0f 85 33 ff 
[   31.324457] RIP  [<ffffffff817752f6>] remove_and_add_spares+0x236/0x310
[   31.324840]  RSP <ffff880084537d40>
[   31.325069] CR2: 0000000000000050
[   31.325311] ---[ end trace ef9ffa4f5b63806d ]---
[   31.325683] Kernel panic - not syncing: Fatal exception



To reproduce:

        git clone git://git.kernel.org/pub/scm/linux/kernel/git/wfg/lkp-tests.git
        cd lkp-tests
        bin/lkp install job.yaml  # job file is attached in this email
        bin/lkp run     job.yaml



Thanks,
Xiaolong