TITLE: BUG: lock held when returning to user space in fuse_lock_inode

[   36.715112] ================================================
[   36.720935] [ BUG: lock held when returning to user space! ]
[   36.726730] 4.9.112-g9e79039 #7 Not tainted
[   36.731032] ------------------------------------------------
[   36.736813] syz-executor724/3814 is leaving the kernel with locks still held!
[   36.744085] 1 lock held by syz-executor724/3814:
[   36.748826]  #0:  (&fi->mutex){+.+.+.}, at: [<ffffffff81938722>] fuse_lock_inode+0xa2/0xd0
[   36.748826]  #1:  (&fi->mutex){+.+.+.}, at: [<ffffffff81938722>] somethingelse+0xa2/0xd0