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

commit: d697415be692349156bca1733648c7cb7f8dad77 ("Core scheduling")
git://bee.sh.intel.com/git/aubrey/fast_idle.git core_scheduling

in testcase: locktorture
with following parameters:

	runtime: 300s
	test: cpuhotplug

test-description: This torture test consists of creating a number of kernel threads which acquire the lock and hold it for specific amount of time, thus simulating different critical region behaviors.
test-url: https://www.kernel.org/doc/Documentation/locking/locktorture.txt


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

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


+---------------------------------------------------------+------------+------------+
|                                                         | 9dd58fe7f8 | d697415be6 |
+---------------------------------------------------------+------------+------------+
| boot_successes                                          | 2          | 4          |
| boot_failures                                           | 2          | 8          |
| BUG:kernel_in_stage                                     | 1          |            |
| invoked_oom-killer:gfp_mask=0x                          | 1          | 4          |
| Mem-Info                                                | 1          | 4          |
| Out_of_memory_and_no_killable_processes                 | 1          | 4          |
| Kernel_panic-not_syncing:System_is_deadlocked_on_memory | 1          | 4          |
| WARNING:at_kernel/sched/sched.h:#sched_cpu_dying        | 0          | 4          |
| RIP:sched_cpu_dying                                     | 0          | 4          |
+---------------------------------------------------------+------------+------------+



[  106.996450] WARNING: CPU: 1 PID: 15 at kernel/sched/sched.h:1777 sched_cpu_dying+0x43a/0x4b0
[  106.997907] Modules linked in: locktorture torture virtio_blk ppdev crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel bochs_drm snd_pcm ttm snd_timer drm_kms_helper snd soundcore joydev pcspkr drm serio_raw i6300esb parport_pc parport ata_generic floppy virtio_pci virtio_ring virtio i2c_piix4 qemu_fw_cfg pata_acpi
[  107.001989] CPU: 1 PID: 15 Comm: migration/1 Not tainted 5.0.0-rc8-00542-gd697415 #22
[  107.003100] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  107.004303] RIP: 0010:sched_cpu_dying+0x43a/0x4b0
[  107.004993] Code: fc ff ff 48 8b bb 50 0c 00 00 e9 2d fc ff ff 48 89 df e8 29 78 ff ff 48 8b 45 c0 48 89 45 b8 8b 45 c8 89 45 b4 e9 5f fc ff ff <0f> 0b e9 f4 fc ff ff 48 8d 55 c0 48 c7 c6 c0 f0 24 b9 4c 89 ff 48
[  107.007648] RSP: 0018:ffffb4598039bd78 EFLAGS: 00010087
[  107.008417] RAX: ffff99fdff0e5a00 RBX: ffff99fddcf22ec0 RCX: dead000000000200
[  107.009433] RDX: ffff99fddcf23910 RSI: ffff99fddcf23910 RDI: ffff99fdff0e5ab0
[  107.010462] RBP: ffffb4598039bdd0 R08: ffff99fddcf23910 R09: 000000000004ce13
[  107.011482] R10: ffffb4598039bcc8 R11: 00000000004fa1e0 R12: 0000000000022ec0
[  107.012502] R13: ffff99fdff0e5a00 R14: ffffffffb8e137e0 R15: ffff99fddcf22ec0
[  107.013522] FS:  0000000000000000(0000) GS:ffff99fddcf00000(0000) knlGS:0000000000000000
[  107.014673] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  107.015492] CR2: 00000000004215e0 CR3: 000000007f1ca000 CR4: 00000000000406e0
[  107.016510] Call Trace:
[  107.017564]  ? sched_cpu_starting+0x1b0/0x1b0
[  107.018402]  cpuhp_invoke_callback+0x86/0x5d0
[  107.019056]  ? cpu_disable_common+0x1cf/0x1f0
[  107.019749]  take_cpu_down+0x60/0x90
[  107.020173]  multi_cpu_stop+0x68/0xe0
[  107.020606]  ? cpu_stopper_thread+0x100/0x100
[  107.021123]  cpu_stopper_thread+0x94/0x100
[  107.021609]  ? smpboot_thread_fn+0x2f/0x1e0
[  107.022105]  ? smpboot_thread_fn+0x74/0x1e0
[  107.022595]  ? smpboot_thread_fn+0x14e/0x1e0
[  107.023104]  smpboot_thread_fn+0x149/0x1e0
[  107.023623]  ? sort_range+0x20/0x20
[  107.024042]  kthread+0x11e/0x140
[  107.024492]  ? kthread_park+0x90/0x90
[  107.024927]  ret_from_fork+0x35/0x40
[  107.025381] ---[ end trace a876bdc6aab2744c ]---


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