FYI, we noticed the following commit (built with gcc-7):

commit: e7fe5357977243d45c3924720b9ac9e218547de8 ("block: remove dead elevator code")
https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git mq-conversions

in testcase: mdadm-selftests
with following parameters:

	disk: 1HDD
	test_prefix: 18



on test machine: qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -m 4G

caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):


+---------------------------------------+------------+------------+
|                                       | 3b954b64a4 | e7fe535797 |
+---------------------------------------+------------+------------+
| boot_successes                        | 8          | 0          |
| boot_failures                         | 0          | 8          |
| WARNING:at_lib/kobject.c:#kobject_put | 0          | 8          |
| RIP:kobject_put                       | 0          | 8          |
+---------------------------------------+------------+------------+



[  185.945851] WARNING: CPU: 1 PID: 226 at lib/kobject.c:707 kobject_put+0x37/0x40
[  185.967988] Modules linked in: multipath loop raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq raid10 raid1 raid0 sr_mod cdrom sg ppdev ata_generic pata_acpi snd_pcm crc32c_intel snd_timer snd soundcore pcspkr serio_raw ata_piix libata i2c_piix4 parport_pc floppy parport ip_tables
[  186.035784] CPU: 1 PID: 226 Comm: kworker/1:3 Not tainted 4.19.0-rc6-00196-ge7fe535 #1
[  186.056359] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  186.076781] Workqueue: events __blk_release_queue
[  186.088576] RIP: 0010:kobject_put+0x37/0x40
[  186.099333] Code: 74 16 48 8d 7b 38 f0 ff 4b 38 0f 88 f4 39 01 00 75 1c 5b e9 3b fe ff ff 48 8b 37 48 89 fa 48 c7 c7 78 c1 39 82 e8 89 a1 6a ff <0f> 0b eb d4 5b c3 f3 c3 90 48 85 ff 74 13 53 48 8d 5f 18 48 89 df
[  186.141300] RSP: 0000:ffffc90000aabe38 EFLAGS: 00010282
[  186.154328] RAX: 0000000000000000 RBX: ffff88013fc00098 RCX: 0000000000000000
[  186.170720] RDX: ffff88013fd1ef40 RSI: ffff88013fd16898 RDI: ffff88013fd16898
[  186.187860] RBP: ffff8800a7b5acd8 R08: 0000000000000000 R09: 0000000000000294
[  186.204226] R10: ffffea0001e37ec0 R11: ffffffff82f81fcd R12: ffffffff828abca0
[  186.220532] R13: 0000000000000000 R14: ffff8800a7b5b588 R15: ffff8800a7b5b590
[  186.236864] FS:  0000000000000000(0000) GS:ffff88013fd00000(0000) knlGS:0000000000000000
[  186.256884] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  186.273342] CR2: 00007fff5295c200 CR3: 000000000260a006 CR4: 00000000000206e0
[  186.292454] Call Trace:
[  186.300707]  blk_mq_sysfs_deinit+0x38/0x60
[  186.313663]  blk_mq_release+0x5e/0x70
[  186.326271]  __blk_release_queue+0x79/0x120
[  186.338980]  process_one_work+0x19c/0x3b0
[  186.351711]  worker_thread+0x3c/0x3b0
[  186.362376]  ? process_one_work+0x3b0/0x3b0
[  186.374365]  kthread+0x11e/0x140
[  186.385058]  ? kthread_associate_blkcg+0xb0/0xb0
[  186.398860]  ret_from_fork+0x35/0x40
[  186.409258] ---[ end trace db5c64132e93355f ]---


To reproduce:

        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        find lib/ | cpio -o -H newc --quiet | gzip > modules.cgz
	bin/lkp qemu -k <bzImage> -m modules.cgz job-script # job-script is attached in this email




Thanks,
lkp