Double writing causes goofys crashes

[remrain]

Goofys crashes when writing the same file simultaneous.

Ex:
date >mount-test/data & date >mount-test/data & date >mount-test/data

2018/08/29 19:51:31.111694 s3.DEBUG HEAD mount-test/data/ = no such file or directory
2018/08/29 19:51:31.111718 fuse.DEBUG <-- LookUpInode 7 data no such file or directory
2018/08/29 19:51:31.111816 fuse.DEBUG Op 0x00000003        connection.go:481] -> Error: "no such file or directory"
2018/08/29 19:51:31.111978 fuse.DEBUG Op 0x00000002        connection.go:396] <- CreateFile (parent 7, name "data")
2018/08/29 19:51:31.112092 fuse.DEBUG Create 7 mount-test [data]
2018/08/29 19:51:31.112144 fuse.DEBUG <-- CreateFile 13 mount-test/data []
2018/08/29 19:51:31.112198 fuse.DEBUG Op 0x00000002        connection.go:479] -> OK (inode 13)
2018/08/29 19:51:31.112380 fuse.DEBUG Op 0x00000003        connection.go:396] <- CreateFile (parent 7, name "data")
2018/08/29 19:51:31.112500 fuse.DEBUG Create 7 mount-test [data]
panic: double insert of mount-test/data

goroutine 177 [running]:
github.com/kahing/goofys/internal.(*Inode).insertChildUnlocked(0xc420114240, 0xc4201d4480)
	/private/tmp/goofys-20180109-35985-h1zbtw/gopath/src/github.com/kahing/goofys/internal/handles.go:246 +0x616
github.com/kahing/goofys/internal.(*Goofys).insertInode(0xc420161ee0, 0xc420114240, 0xc4201d4480)
	/private/tmp/goofys-20180109-35985-h1zbtw/gopath/src/github.com/kahing/goofys/internal/goofys.go:687 +0x53
github.com/kahing/goofys/internal.(*Goofys).CreateFile(0xc420161ee0, 0x4891140, 0xc420262f30, 0xc4208e6000, 0x0, 0x0)
	/private/tmp/goofys-20180109-35985-h1zbtw/gopath/src/github.com/kahing/goofys/internal/goofys.go:973 +0x138
github.com/jacobsa/fuse/fuseutil.(*fileSystemServer).handleOp(0xc42025e140, 0xc420280410, 0x4891140, 0xc420262f30, 0x44bcd60, 0xc4208e6000)
	/private/tmp/goofys-20180109-35985-h1zbtw/gopath/src/github.com/jacobsa/fuse/fuseutil/file_system.go:161 +0x547
created by github.com/jacobsa/fuse/fuseutil.(*fileSystemServer).ServeOps
	/private/tmp/goofys-20180109-35985-h1zbtw/gopath/src/github.com/jacobsa/fuse/fuseutil/file_system.go:122 +0x176