possible deadlock in vfs_fallocate

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger  
crash:

Reported-and-tested-by:  
syzbot+148c2885d71194f18d28 at syzkaller.appspotmail.com

Tested on:

commit:         48b161983ae5 Merge tag 'xarray-5.0-rc3' of git://git.infra..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd3a020d055fa2e8
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16e6d908c00000

Note: testing is done by a robot and is best-effort only.