WARNING: lock held when returning to user space in fuse_lock_inode

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c25c74b7476e Merge tag 'trace-v4.18-rc3-2' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=177bcec2400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
dashboard link: https://syzkaller.appspot.com/bug?extid=3f7b29af1baa9d0a55be
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13aa7678400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17492678400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3f7b29af1baa9d0a55be@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)

================================================
WARNING: lock held when returning to user space!
4.18.0-rc4+ #143 Not tainted
------------------------------------------------
syz-executor012/4539 is leaving the kernel with locks still held!
1 lock held by syz-executor012/4539:
 #0: (____ptrval____) (&fi->mutex){+.+.}, at: fuse_lock_inode+0xaf/0xe0  
fs/fuse/inode.c:363


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