WARNING in fanotify_handle_event

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    963172d9 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17c090eaa00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa9f7e1b6a8bb586
dashboard link: https://syzkaller.appspot.com/bug?extid=c277e8e2f46414645508
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15a32f46a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13a7dc9ea00000

The bug was bisected to:

commit 77115225acc67d9ac4b15f04dd138006b9cd1ef2
Author: Amir Goldstein <amir73il@xxxxxxxxx>
Date:   Thu Jan 10 17:04:37 2019 +0000

    fanotify: cache fsid in fsnotify_mark_connector

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12bfcb66a00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=11bfcb66a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=16bfcb66a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c277e8e2f46414645508@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 77115225acc6 ("fanotify: cache fsid in fsnotify_mark_connector")

WARNING: CPU: 0 PID: 8994 at fs/notify/fanotify/fanotify.c:359  
fanotify_get_fsid fs/notify/fanotify/fanotify.c:359 [inline]
WARNING: CPU: 0 PID: 8994 at fs/notify/fanotify/fanotify.c:359  
fanotify_handle_event+0x5ff/0xc6d fs/notify/fanotify/fanotify.c:418
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 8994 Comm: rs:main Q:Reg Not tainted 5.2.0-rc4+ #27
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+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2cb/0x744 kernel/panic.c:219
 __warn.cold+0x20/0x4d kernel/panic.c:576
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:986
RIP: 0010:fanotify_get_fsid fs/notify/fanotify/fanotify.c:359 [inline]
RIP: 0010:fanotify_handle_event+0x5ff/0xc6d  
fs/notify/fanotify/fanotify.c:418
Code: 06 00 00 8b 5b 40 31 ff 8b b5 fc fe ff ff 09 de 89 b5 f0 fe ff ff e8  
f0 64 ab ff 8b b5 f0 fe ff ff 85 f6 75 55 e8 61 63 ab ff <0f> 0b e8 5a 63  
ab ff 41 83 c6 01 bf 03 00 00 00 44 89 f6 e8 c9 64
RSP: 0018:ffff8880a66dfb80 EFLAGS: 00010293
RAX: ffff888087bf0640 RBX: 0000000000000000 RCX: ffffffff81c55df0
RDX: 0000000000000000 RSI: ffffffff81c55dff RDI: 0000000000000005
RBP: ffff8880a66dfcc8 R08: ffff888087bf0640 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: 0000000000000002 R15: dffffc0000000000
 send_to_group fs/notify/fsnotify.c:271 [inline]
 fsnotify+0x71f/0xbc0 fs/notify/fsnotify.c:409
 fsnotify_path include/linux/fsnotify.h:54 [inline]
 fsnotify_path include/linux/fsnotify.h:47 [inline]
 fsnotify_modify include/linux/fsnotify.h:230 [inline]
 vfs_write+0x4dc/0x580 fs/read_write.c:560
 ksys_write+0x14f/0x290 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+0x73/0xb0 fs/read_write.c:620
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f4cdf18519d
Code: d1 20 00 00 75 10 b8 01 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48  
83 ec 08 e8 be fa ff ff 48 89 04 24 b8 01 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 07 fb ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f4cdd726000 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000155 RCX: 00007f4cdf18519d
RDX: 0000000000000155 RSI: 00000000008bda90 RDI: 0000000000000001
RBP: 00000000008bda90 R08: 6573753a725f7463 R09: 745f656d6f685f72
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00007f4cdd726480 R14: 0000000000000001 R15: 00000000008bd890
Kernel Offset: disabled
Rebooting in 86400 seconds..


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