FYI, we noticed the below changes on

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-testing
commit 3668622c537df68d542cf29e98c05527080e302a ("proc: Allow creating permanently empty directories.")


+----------------------------------------------+------------+------------+
|                                              | de4e98aaa1 | 3668622c53 |
+----------------------------------------------+------------+------------+
| boot_successes                               | 20         | 0          |
| boot_failures                                | 0          | 10         |
| BUG:unable_to_handle_kernel                  | 0          | 10         |
| Oops                                         | 0          | 10         |
| EIP_is_at_d_flags_for_inode                  | 0          | 10         |
| Kernel_panic-not_syncing:Fatal_exception     | 0          | 10         |
| backtrace:vfs_fstatat                        | 0          | 10         |
| backtrace:SyS_fstatat64                      | 0          | 10         |
| WARNING:at_fs/proc/inode.c:#proc_get_inode() | 0          | 4          |
+----------------------------------------------+------------+------------+


[main] Generating file descriptors
[main] Added 55 filenames from /dev
[   16.021609] ------------[ cut here ]------------
[   16.022022] WARNING: CPU: 1 PID: 468 at fs/proc/inode.c:439 proc_get_inode+0x10f/0x120()
[   16.022794] Modules linked in:
[   16.023049] CPU: 1 PID: 468 Comm: trinity-main Not tainted 4.1.0-rc3-00674-geb72c41 #273
[   16.023679] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[   16.024451]  00000001 00000000 4eb49d80 4147e325 00000000 4eb49db4 41052541 41606c5c
[   16.025218]  00000001 000001d4 41612420 000001b7 4117c45f 000001b7 4117c45f 4dd406fc
[   16.025925]  524205d0 4dd4001c 4eb49dc4 410525ed 00000009 00000000 4eb49dd4 4117c45f
[   16.026629] Call Trace:
[   16.026852]  [<4147e325>] dump_stack+0x48/0x60
[   16.027210]  [<41052541>] warn_slowpath_common+0x81/0xb0
[   16.027598]  [<4117c45f>] ? proc_get_inode+0x10f/0x120
[   16.027975]  [<4117c45f>] ? proc_get_inode+0x10f/0x120
[   16.028370]  [<410525ed>] warn_slowpath_null+0x1d/0x20
[   16.028755]  [<4117c45f>] proc_get_inode+0x10f/0x120
[   16.029133]  [<411802e1>] proc_lookup_de+0x41/0xa0
[   16.029486]  [<41180352>] proc_lookup+0x12/0x20
[   16.029842]  [<411322c2>] lookup_real+0x12/0x40
[   16.030198]  [<411329bd>] __lookup_hash+0x2d/0x40
[   16.030547]  [<41134180>] walk_component+0x120/0x630
[   16.030914]  [<41134cd9>] ? path_init+0x169/0x710
[   16.031273]  [<41135074>] ? path_init+0x504/0x710
[   16.031622]  [<411360fe>] path_lookupat+0x9e/0x370
[   16.032019]  [<4111da27>] ? slob_new_pages+0x17/0x40
[   16.032451]  [<411363ef>] filename_lookup+0x1f/0x70
[   16.032811]  [<41138f2b>] user_path_at_empty+0x3b/0x80
[   16.033201]  [<414833e8>] ? mutex_unlock+0x8/0x10
[   16.033551]  [<41138f8a>] user_path_at+0x1a/0x20
[   16.033895]  [<4112d8e8>] vfs_fstatat+0x48/0x90
[   16.034248]  [<4112e32e>] SyS_fstatat64+0x1e/0x40
[   16.034601]  [<4113c102>] ? SyS_getdents64+0x62/0xd0
[   16.034969]  [<4113be30>] ? filldir+0x100/0x100
[   16.035321]  [<414871f1>] ? syscall_exit+0x8/0x21
[   16.035677]  [<414871e5>] syscall_call+0x7/0x7
[   16.036030]  [<41480000>] ? __schedule+0x260/0xa40
[   16.036403] ---[ end trace 57cb8cccefb5fecf ]---
[   16.036764] BUG: unable to handle kernel NULL pointer dereference at   (null)



Thanks,
Ying Huang