Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

On 17/03/2018 08:51, kernel test robot wrote:
> FYI, we noticed the following commit (built with gcc-7):
> 
> commit: b1f0502d04537ef55b0c296823affe332b100eb5 ("mm: VMA sequence count")
> url: https://github.com/0day-ci/linux/commits/Laurent-Dufour/Speculative-page-faults/20180316-151833
> 
> 
> 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 SandyBridge -m 512M
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> +----------------------------------------+------------+------------+
> |                                        | 6a4ce82339 | b1f0502d04 |
> +----------------------------------------+------------+------------+
> | boot_successes                         | 8          | 4          |
> | boot_failures                          | 0          | 4          |
> | INFO:trying_to_register_non-static_key | 0          | 4          |
> +----------------------------------------+------------+------------+
> 
> 
> 
> [   22.212940] INFO: trying to register non-static key.
> [   22.213687] the code is fine but needs lockdep annotation.
> [   22.214459] turning off the locking correctness validator.
> [   22.227459] CPU: 0 PID: 547 Comm: trinity-main Not tainted 4.16.0-rc4-next-20180309-00007-gb1f0502 #239
> [   22.228904] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [   22.230043] Call Trace:
> [   22.230409]  dump_stack+0x5d/0x79
> [   22.231025]  register_lock_class+0x226/0x45e
> [   22.231827]  ? kvm_clock_read+0x21/0x30
> [   22.232544]  ? kvm_sched_clock_read+0x5/0xd
> [   22.233330]  __lock_acquire+0xa2/0x774
> [   22.234152]  lock_acquire+0x4b/0x66
> [   22.234805]  ? unmap_vmas+0x30/0x3d
> [   22.245680]  unmap_page_range+0x56/0x48c
> [   22.248127]  ? unmap_vmas+0x30/0x3d
> [   22.248741]  ? lru_deactivate_file_fn+0x2c6/0x2c6
> [   22.249537]  ? pagevec_lru_move_fn+0x9a/0xa9
> [   22.250244]  unmap_vmas+0x30/0x3d
> [   22.250791]  unmap_region+0xad/0x105
> [   22.251419]  mmap_region+0x3cc/0x455
> [   22.252011]  do_mmap+0x394/0x3e9
> [   22.261224]  vm_mmap_pgoff+0x9c/0xe5
> [   22.261798]  SyS_mmap_pgoff+0x19a/0x1d4
> [   22.262475]  ? task_work_run+0x5e/0x9c
> [   22.263163]  do_syscall_64+0x6d/0x103
> [   22.263814]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> [   22.264697] RIP: 0033:0x4573da
> [   22.267248] RSP: 002b:00007fffa22f1398 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
> [   22.274720] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000004573da
> [   22.276083] RDX: 0000000000000001 RSI: 0000000000001000 RDI: 0000000000000000
> [   22.277343] RBP: 000000000000001c R08: 000000000000001c R09: 0000000000000000
> [   22.278686] R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
> [   22.279930] R13: 0000000000001000 R14: 0000000000000002 R15: 0000000000000000
> [   22.391866] trinity-main uses obsolete (PF_INET,SOCK_PACKET)
> [  327.566956] sysrq: SysRq : Emergency Sync
> [  327.567849] Emergency Sync complete
> [  327.569975] sysrq: SysRq : Resetting

I found the root cause of this lockdep warning.

In mmap_region(), unmap_region() may be called while vma_link() has not been
called. This happens during the error path if call_mmap() failed.

The only to fix that particular case is to call
seqcount_init(&vma->vm_sequence) when initializing the vma in mmap_region().

Thanks,
Laurent.