FYI, we noticed the following commit (built with gcc-4.9):

commit: 6ba0c46abfbfb7f68c34cfb23b042e74e765edbb ("x86/entry/64: Create a percpu SYSCALL entry trampoline")
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git x86/entry_stack.wip

in testcase: trinity
with following parameters:

	runtime: 300s

test-description: Trinity is a linux system call fuzz tester.
test-url: http://codemonkey.org.uk/projects/trinity/


on test machine: qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -m 1G

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


+--------------------------------------------------+------------+------------+
|                                                  | 1559877227 | 6ba0c46abf |
+--------------------------------------------------+------------+------------+
| boot_successes                                   | 2          | 4          |
| boot_failures                                    | 10         | 8          |
| BUG:kernel_hang_in_test_stage                    | 10         | 8          |
| WARNING:at_kernel/locking/lockdep.c:#check_flags | 0          | 8          |
| RIP:check_flags                                  | 0          | 8          |
+--------------------------------------------------+------------+------------+



[   33.178620] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:3911 check_flags+0x1d4/0x1e0
[   33.180175] Modules linked in:
[   33.180679] CPU: 0 PID: 1 Comm: init Not tainted 4.14.0-rc7-00077-g6ba0c46 #1
[   33.181804] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[   33.183111] task: ffff880032e44040 task.stack: ffffc90000008000
[   33.184064] RIP: 0010:check_flags+0x1d4/0x1e0
[   33.184751] RSP: 0018:ffffc9000000bea0 EFLAGS: 00010086
[   33.185629] RAX: 000000000000002e RBX: ffff880032e44040 RCX: 0000000000000000
[   33.186743] RDX: 0000000000000000 RSI: ffffffff810d527d RDI: 0000000000000000
[   33.187880] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   33.188993] R10: 0000000000000000 R11: ffffffff810d5239 R12: 0000000000000000
[   33.190123] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
[   33.191245] FS:  0000000000000000(0000) GS:ffffffff81e3b000(0000) knlGS:0000000000000000
[   33.192501] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   33.193421] CR2: 00007f12a97a2100 CR3: 000000003f43d000 CR4: 00000000000006b0
[   33.194541] Call Trace:
[   33.194935]  lock_acquire+0x55/0x1b0
[   33.195546]  vtime_user_exit+0x3c/0xa0
[   33.196147]  ? __context_tracking_exit+0x6f/0x1a0
[   33.196891]  __context_tracking_exit+0x6f/0x1a0
[   33.197621]  do_syscall_64+0x35b/0x550
[   33.198219]  entry_SYSCALL64_slow_path+0x25/0x25
[   33.198969] RIP: 0033:0x7f12a95951f9
[   33.199548] RSP: 002b:00007ffd91c847a8 EFLAGS: 00000246 ORIG_RAX: 000000000000000c
[   33.200747] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f12a95951f9
[   33.201857] RDX: 00007ffd91c84a70 RSI: 000055dd96c392c0 RDI: 0000000000000000
[   33.202971] RBP: 000055dd96c06040 R08: 0000000000000001 R09: 00007ffd91c84a99
[   33.204093] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000009
[   33.205201] R13: 00007f12a957e850 R14: 0000000000000001 R15: 0000000000001000
[   33.206335] Code: 81 48 c7 c7 62 5e c2 81 31 c0 e8 4c e4 00 00 0f ff e9 dd fe ff ff 48 c7 c6 7f 57 c3 81 48 c7 c7 62 5e c2 81 31 c0 e8 30 e4 00 00 <0f> ff e9 0e ff ff ff 0f 1f 44 00 00 41 57 41 56 41 55 41 54 55 
[   33.209395] ---[ end trace 89cbd096682c3c22 ]---


To reproduce:

        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        bin/lkp qemu -k <bzImage> job-script  # job-script is attached in this email



Thanks,
Xiaolong