WARNING in notify_change

[syzbot <syzbot+2b74da47f048a5046135@syzkaller.appspotmail.com>]

Hello,

syzbot hit the following crash on upstream commit
3fd14cdcc05a682b03743683ce3a726898b20555 (Fri Apr 6 19:15:41 2018 +0000)
Merge tag 'mtd/for-4.17' of git://git.infradead.org/linux-mtd
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=2b74da47f048a5046135

So far this crash happened 3 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5084712116682752
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=6394049002995712
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=4711531803574272
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5813481738265533882
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2b74da47f048a5046135@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

WARNING: CPU: 1 PID: 4470 at fs/attr.c:213 notify_change+0xd94/0x10c0  
fs/attr.c:213
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 4470 Comm: syzkaller570118 Not tainted 4.16.0+ #4
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+0x1b9/0x294 lib/dump_stack.c:113
  panic+0x22f/0x4de kernel/panic.c:183
  __warn.cold.8+0x163/0x1a3 kernel/panic.c:547
  report_bug+0x252/0x2d0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  do_error_trap+0x1de/0x490 arch/x86/kernel/traps.c:296
  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
  invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:991
RIP: 0010:notify_change+0xd94/0x10c0 fs/attr.c:213
RSP: 0018:ffff8801ad76f860 EFLAGS: 00010293
RAX: ffff8801d9f66680 RBX: ffff8801d32d4630 RCX: ffffffff81c36578
RDX: 0000000000000000 RSI: ffffffff81c371b4 RDI: 0000000000000007
RBP: ffff8801ad76f930 R08: ffff8801d9f66680 R09: ffffed003a65a8e2
R10: ffffed003a65a8e2 R11: ffff8801d32d4717 R12: 0000000000004200
R13: ffff8801ad76f970 R14: ffff8801d5260ce0 R15: 1ffff10035aedf18
  __remove_privs fs/inode.c:1813 [inline]
  file_remove_privs+0x2bf/0x530 fs/inode.c:1835
  __generic_file_write_iter+0x169/0x5e0 mm/filemap.c:3209
  blkdev_write_iter+0x233/0x420 fs/block_dev.c:1908
  call_write_iter include/linux/fs.h:1782 [inline]
  new_sync_write fs/read_write.c:474 [inline]
  __vfs_write+0x5bc/0x880 fs/read_write.c:487
  vfs_write+0x1f8/0x560 fs/read_write.c:549
  ksys_write+0xf9/0x250 fs/read_write.c:598
  SYSC_write fs/read_write.c:610 [inline]
  SyS_write+0x24/0x30 fs/read_write.c:607
  do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x445c59
RSP: 002b:00007f76203b7d38 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 0000000000445c59
RDX: 0000000000000050 RSI: 0000000020000400 RDI: 0000000000000008
RBP: 0000000000000005 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00000000006dac20
R13: 0000000000000006 R14: 0030656c69662f2e R15: 0000000000000000
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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