Re: WARNING in kernfs_create_dir_ns

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    72825454 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=104d6755a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
dashboard link: https://syzkaller.appspot.com/bug?extid=38f5d5cf7ae88c46b11a
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12a6c439a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1353c323a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+38f5d5cf7ae88c46b11a@xxxxxxxxxxxxxxxxxxxxxxxxx

WARNING: CPU: 0 PID: 8613 at fs/kernfs/dir.c:493 kernfs_get  
fs/kernfs/dir.c:493 [inline]
WARNING: CPU: 0 PID: 8613 at fs/kernfs/dir.c:493 kernfs_new_node  
fs/kernfs/dir.c:700 [inline]
WARNING: CPU: 0 PID: 8613 at fs/kernfs/dir.c:493  
kernfs_create_dir_ns+0x205/0x230 fs/kernfs/dir.c:1022
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 8613 Comm: syz-executor696 Not tainted 5.2.0-rc6+ #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
 panic+0x28a/0x7c9 kernel/panic.c:219
 __warn+0x216/0x220 kernel/panic.c:576
 report_bug+0x190/0x290 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 do_error_trap+0xd7/0x450 arch/x86/kernel/traps.c:272
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:986
RIP: 0010:kernfs_get fs/kernfs/dir.c:493 [inline]
RIP: 0010:kernfs_new_node fs/kernfs/dir.c:700 [inline]
RIP: 0010:kernfs_create_dir_ns+0x205/0x230 fs/kernfs/dir.c:1022
Code: ff 4c 89 ff e8 7c cd ff ff 4c 63 fb eb 05 e8 22 27 9a ff 4c 89 f8 48  
83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 0b 27 9a ff <0f> 0b e9 e9 fe  
ff ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c be fe ff
RSP: 0018:ffff88808d26f730 EFLAGS: 00010293
RAX: ffffffff81db8a95 RBX: ffff88809e5252a0 RCX: ffff88808a4aa000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88808d26f768 R08: ffffffff81db8977 R09: ffffed1013ca4a55
R10: ffffed1013ca4a55 R11: 1ffff11013ca4a54 R12: ffff888098a8a200
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff8880a339e620
 sysfs_create_dir_ns+0x161/0x300 fs/sysfs/dir.c:59
 create_dir lib/kobject.c:89 [inline]
 kobject_add_internal+0x459/0xd50 lib/kobject.c:255
 kobject_add_varg lib/kobject.c:390 [inline]
 kobject_add+0x138/0x200 lib/kobject.c:442
 device_add+0x508/0x1570 drivers/base/core.c:2062
 hci_register_dev+0x331/0x6c0 net/bluetooth/hci_core.c:3305
 __vhci_create_device drivers/bluetooth/hci_vhci.c:124 [inline]
 vhci_create_device+0x2d1/0x510 drivers/bluetooth/hci_vhci.c:148
 vhci_get_user drivers/bluetooth/hci_vhci.c:204 [inline]
 vhci_write+0x3ac/0x440 drivers/bluetooth/hci_vhci.c:284
 call_write_iter include/linux/fs.h:1872 [inline]
 new_sync_write fs/read_write.c:483 [inline]
 __vfs_write+0x617/0x7d0 fs/read_write.c:496
 vfs_write+0x227/0x510 fs/read_write.c:558
 ksys_write+0x16b/0x2a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:620
 do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441279
Code: e8 ac e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffa3738588 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441279
RDX: 0000000000000002 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 000000000000ef5c R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000401ff0
R13: 0000000000402080 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..