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

commit: a1e6b3dc1c6fadc388e71815c4d85b9a2100ad3f ("[PATCH] debugfs: remove no need inc_nlink")
url: https://github.com/0day-ci/linux/commits/yangerkun/debugfs-remove-no-need-inc_nlink/20181222-210250


in testcase: boot

on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 8G

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


+-----------------------------------+------------+------------+
|                                   | 16df1456aa | a1e6b3dc1c |
+-----------------------------------+------------+------------+
| boot_successes                    | 10         | 0          |
| boot_failures                     | 0          | 6          |
| WARNING:at_fs/inode.c:#drop_nlink | 0          | 6          |
| RIP:drop_nlink                    | 0          | 6          |
+-----------------------------------+------------+------------+



[   89.144904] WARNING: CPU: 1 PID: 404 at fs/inode.c:285 drop_nlink+0x24/0x30
[   89.162978] Modules linked in: sr_mod cdrom sg ppdev crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel snd_pcm ata_generic snd_timer pata_acpi aesni_intel crypto_simd snd cryptd glue_helper soundcore pcspkr serio_raw ata_piix libata i2c_piix4 parport_pc floppy parport ip_tables
[   89.201228] CPU: 1 PID: 404 Comm: mount.nfs Not tainted 4.20.0-rc5-00017-ga1e6b3d #1
[   89.220491] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[   89.230741] RIP: 0010:drop_nlink+0x24/0x30
[   89.238571] Code: 84 00 00 00 00 00 66 66 66 66 90 8b 47 48 85 c0 8d 50 ff 74 15 85 d2 89 57 48 75 0c 48 8b 47 28 f0 48 ff 80 a0 04 00 00 f3 c3 <0f> 0b c7 47 48 ff ff ff ff c3 66 90 66 66 66 66 90 8b 47 48 85 c0
[   89.266513] RSP: 0000:ffffc9000123ba18 EFLAGS: 00010246
[   89.272470] RAX: 0000000000000000 RBX: ffff88821cc6a250 RCX: 0000000000000000
[   89.278356] RDX: 00000000ffffffff RSI: 0000000016694e00 RDI: ffff88821cc6a250
[   89.290053] RBP: ffffc9000123ba40 R08: 0000000000000000 R09: 0000000000000000
[   89.298101] R10: ffffea00089296c0 R11: 0000000000000545 R12: ffff8881f72e8000
[   89.307078] R13: ffff88822ac05bc0 R14: ffff8881f72e8d60 R15: ffff8881f72e80a0
[   89.313889] FS:  00007fc0e6bae480(0000) GS:ffff88823fd00000(0000) knlGS:0000000000000000
[   89.323184] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   89.332486] CR2: 00007fc0e56082f0 CR3: 00000001f2fe6000 CR4: 00000000000406e0
[   89.341276] Call Trace:
[   89.346649]  simple_unlink+0x48/0x60
[   89.351926]  simple_rmdir+0x2d/0x50
[   89.357466]  __debugfs_remove+0x45/0xc0
[   89.364558]  debugfs_remove_recursive+0x185/0x1c0
[   89.370362]  rpc_clnt_debugfs_unregister+0x15/0x30
[   89.377695]  rpc_free_client+0x34/0xf0
[   89.383292]  rpc_release_client+0x54/0x90
[   89.387923]  rpc_shutdown_client+0x89/0x170
[   89.392889]  ? rpc_call_sync+0x65/0x90
[   89.400248]  nfs_mount+0x148/0x2a0
[   89.404366]  nfs_request_mount+0xf4/0x1c0
[   89.410765]  nfs_try_mount+0xba/0x2c0
[   89.415208]  ? _cond_resched+0x19/0x30
[   89.418969]  ? __kmalloc_track_caller+0x58/0x240
[   89.423842]  ? _cond_resched+0x19/0x30
[   89.427552]  nfs_fs_mount+0x63f/0xd10
[   89.431874]  ? pcpu_alloc_area+0xc0/0x130
[   89.435924]  ? nfs_clone_super+0x70/0x70
[   89.439891]  ? param_set_portnr+0x70/0x70
[   89.444260]  ? mount_fs+0x35/0x150
[   89.447301]  ? nfs_remount+0x350/0x350
[   89.450778]  mount_fs+0x35/0x150
[   89.454335]  vfs_kern_mount+0x54/0x120
[   89.458249]  do_mount+0x5e8/0xcb0
[   89.461669]  ? kmem_cache_alloc_trace+0x3e/0x1e0
[   89.467487]  ksys_mount+0x80/0xd0
[   89.471994]  __x64_sys_mount+0x21/0x30
[   89.476396]  do_syscall_64+0x5b/0x180
[   89.480757]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   89.485757] RIP: 0033:0x7fc0e626a24a
[   89.489684] Code: 48 8b 0d 51 fc 2a 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 1e fc 2a 00 f7 d8 64 89 01 48
[   89.513383] RSP: 002b:00007fffc13beeb8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[   89.522200] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc0e626a24a
[   89.530213] RDX: 000055c80420af90 RSI: 000055c80420af70 RDI: 000055c804209230
[   89.537245] RBP: 00007fffc13bf0b0 R08: 000055c804216340 R09: 0000000000000060
[   89.544541] R10: 0000000000000000 R11: 0000000000000206 R12: 00007fc0e6bae410
[   89.552178] R13: 00007fffc13bf0b0 R14: 00007fffc13befb0 R15: 000055c804216320
[   89.560460] ---[ end trace 55911a8453dafee2 ]---


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,
lkp